Since Castlevania is such an established and long-running series, I should probably preface this by saying that Order of Ecclesia is the first one I have played. As such, I can't offer any comparison between this and its predecessors.
The line between challenging and infuriating is incredibly thin; Castlevania: Order of Ecclesia walks it like a tightrope. At times I felt frustrated and annoyed, yet I can't help but appreciate it as a solidly built side-scrolling action/RPG with strong character and flair.
The game's events centre on Shanoa, a member of the titular order who has been chosen to use the Dominus Glyph (the most powerful of glyphs, more on those later) to destroy Dracula. Things, as they generally do in these situations, go awry. Dominus is stolen and after some kerfuffle, Shanoa sets off on her quest to retrieve it. The plot is, for the most part, a drossy vehicle which exists simply to accommodate the hacking and slashing. I will say, though, that considering the material, the exposition is neither drawn-out nor imposing - which it easily could have been.*
Along her way, Shanoa passes through a wide variety of locales, at the heart of which is Wygol Village. More and more areas become unlocked as you progress but there is always only one which you need to visit; the main quest is resoundingly linear. This is assuaged by the aforementioned village, which serves as a side-quest hub. At first it is seemingly abandoned but on your travels you will, one by one, locate its inhabitants who have been kidnapped. Their quests become available as they are rescued, the rewards for which are quite worthwhile. This system works out well as there is generally always something you can do should you get bored of being face-rolled by a particularly challenging new area. Irksomely, there is a point in the storyline where if you, by then, have not rescued the entire populace, the game will prematurely end - after a boss battle, no less! This isn't hugely necessary and only serves as a frustration should you encounter it.**
On the subject of boss battles, they are, by and large, the stars of the show. The first few will likely be beaten with a single attempt but they quickly become a big challenge. Most will require several tries in order to become accustomed to their attacks and to figure out which of yours are best suited for the occasion. They are extremely well tuned and rarely become frustrating as the pattern of attack never seems unfair. When you die, it's because you didn't react to something correctly and, thanks to well-placed save points, if you do die, it's no big deal. Also, every boss room is marked with a special door so there's no danger of inadvertently wandering into one and having to redo a whole area. Medals are awarded to those who defeat a boss without losing a single hit point, though collecting them all is certainly for the more hardcore of gamers.***
The game itself is arguably aimed at dedicated players, the difficulty being several steps above the norm.**** As well as the bosses, regular enemies will begin to pose a serious threat as the game progresses. This is mostly due to the variety of your ever-expanding arsenal of abilities. There are seven types of damage and enemies are generally resistant or weak to a few of them. Upon entering a new area, most of your efforts will be spent on figuring these out and deciding which combination of attacks and defences form the best strategy. The logistics of inflicting said damage is also a significant part of the equation; weapons differ in range and speed and every magic spell has its own method of delivery.
Swords, maces, fireballs, lightning bolts, any of your physical or magical attacks are all housed within glyphs which you can either find, or absorb from enemies as they use them. One glyph is equipped in each hand, allowing for tailor-made combos. On top of this, glyphs can be combined to form glyph unions - especially powerful attacks resulting from the amalgamation of both types of damage. For example, you could equip a sword glyph and ice glyph and use the union to execute a strong icy slash. Finally, a miscellaneous glyph is bound to the shoulder button. These offer a wide variety of effects such as boosting stats, increasing movement speed or even physical transformation. All this results in there often being more than one valid strategy for any given situation; a large part of the fun is discovering what these may be.
Even at two years old, this is probably still one of the best looking games on the DS. Though all the tile sets are recoloured and recycled at least once during the course of the game, character is one thing which they do not lack. Misty mountains, aquatic caves, frozen waterfalls and, naturally, Dracula's Castle - all are well-presented; there is a particularly great area which features a raging sea as its backdrop. Spell and weapon animations are great though characters' appearances are a bit hit and miss. While Shanoa herself looks splendid, it's obvious that some enemy sprites have been taken from older games in the series and copy/pasted in. The bosses however are appropriately monstrous and awesome. A gothic style pervades all aspects of the game's visuals and is exceptionally appropriate. The soundtrack is predominantly orchestral, with strong melodies which you would expect from game music. It has some metal influences in places which meshes well with the overarching gothic theme. It's quite memorable and one of the better game scores I've come across, though I will say it doesn't immediately grab you.
And that, is my overall feeling about this game. It's not something I spent a huge amount of time with at first but, as I progressed, it became more and more engrossing. The save file read roughly 14 hours in the end, but that doesn't count the failed attempts at various boss fights and tricky areas. Realistically it's closer 17 or 18 - a great length for something on a handheld.***** My main gripe is that the difficulty can be off-putting. As I said earlier, it doesn't seem unfair at any point, but a lot of that depends on your mood. If you're looking for something to relax with, it isn't the right choice... but if you want some challenging action with a great combat system and aesthetic, then it probably is.
* I'm looking at you, Final Fantasy 13.
** I'd imagine anyone familiar with Castlevania's style of level design won't have this problem. I only realized half way through that certain walls can be bashed open to reveal hidden rooms.
*** I managed to get one and, considering the fight, it was basically free anyway.
**** Thankfully nowhere near as unforgiving as, say, Ninja Gaiden.
***** Keep in mind this is my first Castlevania game, those familiar with the series will probably take a few hours less.
The line between challenging and infuriating is incredibly thin; Castlevania: Order of Ecclesia walks it like a tightrope. At times I felt frustrated and annoyed, yet I can't help but appreciate it as a solidly built side-scrolling action/RPG with strong character and flair.

The game's events centre on Shanoa, a member of the titular order who has been chosen to use the Dominus Glyph (the most powerful of glyphs, more on those later) to destroy Dracula. Things, as they generally do in these situations, go awry. Dominus is stolen and after some kerfuffle, Shanoa sets off on her quest to retrieve it. The plot is, for the most part, a drossy vehicle which exists simply to accommodate the hacking and slashing. I will say, though, that considering the material, the exposition is neither drawn-out nor imposing - which it easily could have been.*
Along her way, Shanoa passes through a wide variety of locales, at the heart of which is Wygol Village. More and more areas become unlocked as you progress but there is always only one which you need to visit; the main quest is resoundingly linear. This is assuaged by the aforementioned village, which serves as a side-quest hub. At first it is seemingly abandoned but on your travels you will, one by one, locate its inhabitants who have been kidnapped. Their quests become available as they are rescued, the rewards for which are quite worthwhile. This system works out well as there is generally always something you can do should you get bored of being face-rolled by a particularly challenging new area. Irksomely, there is a point in the storyline where if you, by then, have not rescued the entire populace, the game will prematurely end - after a boss battle, no less! This isn't hugely necessary and only serves as a frustration should you encounter it.**

On the subject of boss battles, they are, by and large, the stars of the show. The first few will likely be beaten with a single attempt but they quickly become a big challenge. Most will require several tries in order to become accustomed to their attacks and to figure out which of yours are best suited for the occasion. They are extremely well tuned and rarely become frustrating as the pattern of attack never seems unfair. When you die, it's because you didn't react to something correctly and, thanks to well-placed save points, if you do die, it's no big deal. Also, every boss room is marked with a special door so there's no danger of inadvertently wandering into one and having to redo a whole area. Medals are awarded to those who defeat a boss without losing a single hit point, though collecting them all is certainly for the more hardcore of gamers.***
The game itself is arguably aimed at dedicated players, the difficulty being several steps above the norm.**** As well as the bosses, regular enemies will begin to pose a serious threat as the game progresses. This is mostly due to the variety of your ever-expanding arsenal of abilities. There are seven types of damage and enemies are generally resistant or weak to a few of them. Upon entering a new area, most of your efforts will be spent on figuring these out and deciding which combination of attacks and defences form the best strategy. The logistics of inflicting said damage is also a significant part of the equation; weapons differ in range and speed and every magic spell has its own method of delivery.

Swords, maces, fireballs, lightning bolts, any of your physical or magical attacks are all housed within glyphs which you can either find, or absorb from enemies as they use them. One glyph is equipped in each hand, allowing for tailor-made combos. On top of this, glyphs can be combined to form glyph unions - especially powerful attacks resulting from the amalgamation of both types of damage. For example, you could equip a sword glyph and ice glyph and use the union to execute a strong icy slash. Finally, a miscellaneous glyph is bound to the shoulder button. These offer a wide variety of effects such as boosting stats, increasing movement speed or even physical transformation. All this results in there often being more than one valid strategy for any given situation; a large part of the fun is discovering what these may be.
Even at two years old, this is probably still one of the best looking games on the DS. Though all the tile sets are recoloured and recycled at least once during the course of the game, character is one thing which they do not lack. Misty mountains, aquatic caves, frozen waterfalls and, naturally, Dracula's Castle - all are well-presented; there is a particularly great area which features a raging sea as its backdrop. Spell and weapon animations are great though characters' appearances are a bit hit and miss. While Shanoa herself looks splendid, it's obvious that some enemy sprites have been taken from older games in the series and copy/pasted in. The bosses however are appropriately monstrous and awesome. A gothic style pervades all aspects of the game's visuals and is exceptionally appropriate. The soundtrack is predominantly orchestral, with strong melodies which you would expect from game music. It has some metal influences in places which meshes well with the overarching gothic theme. It's quite memorable and one of the better game scores I've come across, though I will say it doesn't immediately grab you.
And that, is my overall feeling about this game. It's not something I spent a huge amount of time with at first but, as I progressed, it became more and more engrossing. The save file read roughly 14 hours in the end, but that doesn't count the failed attempts at various boss fights and tricky areas. Realistically it's closer 17 or 18 - a great length for something on a handheld.***** My main gripe is that the difficulty can be off-putting. As I said earlier, it doesn't seem unfair at any point, but a lot of that depends on your mood. If you're looking for something to relax with, it isn't the right choice... but if you want some challenging action with a great combat system and aesthetic, then it probably is.
* I'm looking at you, Final Fantasy 13.
** I'd imagine anyone familiar with Castlevania's style of level design won't have this problem. I only realized half way through that certain walls can be bashed open to reveal hidden rooms.
*** I managed to get one and, considering the fight, it was basically free anyway.
**** Thankfully nowhere near as unforgiving as, say, Ninja Gaiden.
***** Keep in mind this is my first Castlevania game, those familiar with the series will probably take a few hours less.