Hmmm, some of the tactical errors tend to be explained during the storyline. Video games as a medium suffer from a lot of the same limitations in storytelling as TV and movies, where characters ALSO do a lot of things that make little or no sense. The problem is that this kind of medium doesn't really let you get into the heads of those involved, or give you a good view of what the people involved actually know. You just get to see the end results. It's sort of like when you watch a movie based on a book you've read, and watch a situation you recognize from the book and while it looks pretty accurate to what you'd imagine, it comes accross as lacking due to a complete lack of subtext or perspective on the events occuring.
There are plenty of cases where things that are just plain stupid happen for the sake of moving on a plot, but in many more it's simply a matter of trying to deal with situations requiring a depth which the medium is not capable of. It's also important to know that characters in a story do not have the advantage of your omniscient perspective as the person watching the story unfold. Military intelligence is a big deal IRL, and honestly just because you as a spectator know the true extent of a threat or what tactics would work against it does NOT mean that the characters in the story have the same insights. In things like "Dragon Age: Origins" the battle of Ostragar makes sense when you consider that the king is being set up, Loghain is setting things up specifically to kill the king, and having information intentionally held back towards that end. Loghain himself underestimates the threat posed by the Darkspawn, and sees the King as a greater threat due to his dealings with Orlais. If everyone involved had your perspective as the game player they doubtlessly have made other desciains, but you have to remember that they don't have access to this information.
I cases like the Reapers in "Mass Effect" it's important to think about things realistically. Logistics and money a a major factor in deploying military forces. You can't have them jumping at every shadow out there, you have them reacting to the wrong things and it causes a lot of problems, especially when there are clear and present dangers people know about. It's one of those situations where your perspective as an omniscient player of the game lets you know what a huge threat the reapers are, however from the perspective of those making the desicians there is no real evidence of a threat on that scale, there was Sovreign, but it was destroyed, and no way to prove it didn't act alone. Sure you have Shepard's word for it, but don't forget he was killed pretty soon after the events of the first game, and being dead he wasn't there to actively promote the information he had even if there were other witnesses. It's quite probable the way he was targeted by the keepers was intentional, and exactly for that reason. If he wasn't dead things would have probably developed differantly between Mass Effect 1 and 2.
Or simply, in Mass Effect terms, your making a desician: You've got all these colony worlds to protect, space pirate problems, criminals, and everything else. You get a report from a source that is pretty reliable that there is this threat that should take priority over all those other duties and that you should gather up all your fleets and get ready for it at the expense of their regular duties. This source however dies in what seems to be routine duty, and you OTHER reliable sources (all your spies, intelligence agents, etc...) can't confirm anything that the original source said in any tangible way. Remember that even the other "eye witnesses" lack the advantage of having had a prothean beacon in their head and the exact perspective/translation of what was revealed to Shepard as well.
Now remember, this is your responsibility. By choosing to respond to a threat you heard about but can't verify, fro a source that no longer exists, it means your going to be letting a lot of people die when you committ your fleet to it. Ships that would be out pirate hunting aren't going to be doing it, they are going to be looking for this bigger threat that nobody can find, or spend a lot more time than normal being refitted for a battle of that scale that could be spent using the ships (by trying to get them all updated at once), when even without refits and the like they do their jobs well. Simply put people are going to die. If it's to avert a bigger threat where a lot more people would die it's worthwhile, but if you do this and no threat like that materializes, that makes you an idiot and directly responsible for giving the pirates and other elements those ships kept in line a free lunch pass while you were looking for something that didn't exist. Think of all the criticisms out there about pointless money being spent on military manuvers and operations with no verifyable results, this is like that but on a much larger scale.
See in the situation in Mass Effect, if I was making the desician, with what the guys in charge of the fleets actually know and can verify (as opposed to what I as the player know), I'd probably wind up making a lot of the same desicians. I'd be wrong, of course, but I'd do it thinking I was making the right call at the time, given very little in the way of actual proof other than the word of a dead man who had alien tech in his brain and had problems understanding what it was trying to tell him a lot of the time. If he was still there to deal with, and the data could be analyzed with mental techniques and things that would be one thing, but he's not.
A bit of rambling based on those two points that were raised in response, but I'm just saying I think the positions there can be justified. I don't think there was any paticular stupidity involved in the storylike of either DA:Origns or Mass Effect, as far as those plot points go. Admittedly it could probably have been written better.
Also, for the guy who mentioned it was kind of stupid to have wardogs run out ahead... ummm yeah, that's generally the idea of wardogs, to soak up part of the enemy charge.
Truthfully like a lot of fantasy games (pnp or computer games) the whole "order of battle" depicted is just garbage in general. if you look at it from any kind of technical perspective very little of what we see of "The Battle Of Ostragar" makes a whole heck of a lot of sense, but then again it was meant to be a cinematic to show "yes there was a battle, the good guys lost" to really break it down into a full confrontation using realistic tactics would probably have involved a lot of time and effort that could have been better spent on other aspects of the game... since really the point of the sequence is to set up the plot for your Gray Warden more than anything.
Besides, I think there would be some outrage if along with the dogs they forced a bunch of serfs, peasants, prisoners, and perhaps dreg mercenaries out in an mob ahead of the actual troops to also soak up the charge and act as arrow fodder, while the "important" troops
came in afterwards.
It's also admittedly a lot less cinematically pleasing to watch things like Phalanxs in action, which is why in movies like "300" they demonstrated it, but then found reasons to make the rest of the fight scenes have nothing to do with things like formation or disapline, and instead deal with a bunch of he-men flexing around with weapons doing the action hero thing. It's cooler for a movie, and the same kind of applies for video games. Many people might find the constant portrayal of realistic tactics entertaining and exciting, but I think those people are outnumbered by those who prefer a far more... theatrical presentation. Simply put soldiers replaced warriors on the field of battle, but warriors are far more entertaining to show, or tell stories about for the most part.
