Dungeons and Dragons Online
This game is absolutely wonderful because it does so many things right and differently from the general trend of mmos. Yes it uses the hotkey method like every other mmo and their dog, however it also touches the somewhat less commonly used hack-n-slash via mouse clicks as enemies do not stand in one place. When using ranged weapons/attacks it kind of turns into a 1st/3rd person shooter to a small degree in that you fire it off in the direction you are pointing unless you are targeting them already(override autolock optional).
What I love most about the game though is the way they crafted the enviorment.
Firstly its made with 3 dimensions in mind. Jumping, swimming, and climbing are all used to break up the monotony found in many other MMOs where you are essentially glued to the ground with jumping being there just to create the illusion of 3d movement, and can only break away via flying that is essentially limited No-cliping. They have no problem with putting a switch at the top of a room over a pit of acid with the only way to reach it being to navigate a series of suspended pipes and such that you can fall off of. Or they might obscure a switch behind a tapestry and you must be observant enough to locate it since you can just sweep the room with your mouse. You might swim down through a watery passage to access a otherwise hidden area or alternative route. And this without considering the potential for traps...(or on that later)
Secondly, They finally make a rogue class feel like a rogue. In this game they do more than just DPS, they are one of the two classes that can actually disarm traps (though they are far better at it) which can be found in many places which pose a Serious threat to your party. If you are not careful those traps WILL wipe your party unless they are disarmed. They also tend to be the most gymnastic and best equipped (stat wise) to handle any tricky traps that involve careful movement. They may not be as flashy as rogue like classes in other games, but this rogue actually embraces what it means to be a rogue beyond sneak+stab&stab. I should also mention that the other classes are also very interesting to play as (my favorite is the artificer).
Thirdly, Teamwork is more than just Tank,DPS,Healbot. Some classes like the rogue are needed in order to complete quests due to traps, other times you need to split up and have the two groups deal with different things at the same time (one might have to solve a physical puzzle while the other has to fend off bad guys. Or someone might be needed because they have a high Diplomacy skill and they are the only way you can access someone without resorting to brute force.
Fourthly is the setting itself. I love the Eberron setting to death and this game creates a nice representation of it. It is a perfect one, no. Is it the one I imagined, no. But it is a nicely made one with a healthy respect for the source material (both eberron and D&D).
Finally (for this post anyway), I love how no piece of content is entirely out of the players reach. As a FTP model, some content is freely available to all, while others must be unlocked via micro transactions. This include a number of adventure packs, several classes, races, boosters (to speed your progress but not over power you), and other little tid-bits. While they are straight up free, they can be obtained by someone without spending so much as a penny. Simply by playing the game you get reputation and with reputation you get free turbine points at set amounts. With those points you can buy anything in the DDOStore. While you can only get so many free points from a given realm, you can play on another realm to get more points since Points and most purchases carry over from realm to realm. You also can unlock some material simply as part of earning reputation, though that method only unlocks on that server. In short you get what you give and with a little extra.
There is a lot more about the game i like, but these are the more dominant things i can think of.
Also, Guild owned Airships!