Spoilers will abound:
From the start, the Mass Effect trilogy was positioned to try to fill a hole, which was the lack of space-themed — as opposed to fantasy-themed — RPGs. Mass Effect did that reasonably well. It certainly had its flaws, as the Mako was terrible, exploration a bit dull and boring because of that and because of how the planets were a bit deserted, and the story did have a number of holes in it. But these were things that needed to be fixed, but to me the core idea was good: the universe was interesting, the main character interesting, the support characters had potential, you had to make roleplaying choices, and the story had potential. If they had simply built on that base, there is no way that ME1 would have ended up being my favourite in the series.
And yet, it is. This is because ME2, instead of patching up the existing problems, pretty much went in a completely different direction than ME1 … and that new direction, at least to me, was clearly in the wrong direction every time they did it. They made the exploration more important and yet really, really annoying. They changed the combat mechanics in a manner that, again, really irritated me. They added restrictions and resource management — like fuel — that served no purpose except to annoy. The story went off the rails from the start (when your second game starts with killing you and raising you from the dead, that’s probably not a good sign). Cerberus was given extreme prominence for a group that for the most part in the first game was just there to do horribly flawed experiments that gave you missions to run to get more XP, without really doing an intelligent bridge between the fact that most of the time they killed lots and lots of humans to becoming a group dedicated to humanity.
The only thing they did better in ME2 was the focus on characters. While I can’t say that Mordin, say, is a better character than Tali or Garrus, you are indeed encouraged to talk to them more and make their specific personalities and issues more important to you than you did in ME1. Unfortunately, ME2’s plot is all about doing that, as you flit from specific recruitment mission to recruitment mission to intermission-style missions that were usually about recruiting people, too. Building the team was a nice touch … but it seemed to me that that was all ME2 was about.
ME3 tried to bridge the gap, here, and provide the strong character focus of ME2 inside a strong plot like ME1 had. It failed. It was far less blatant about recruitment than ME2, and that’s given less importance, but the plot is very basic, very standard, and not very deep or very deeply explored. What was good about its plot is all what’s tied into the character arcs: the Genophage, the Quarian/Geth war, EDI and Joker, and so on. But nothing else was that great. The entire ending felt hollow to me … even Anderson’s death seemed to have little impact, especially since it was a bit trite. The exploration system was improved but not fixed, as was the combat system and, well, pretty much everything, in fact. Ultimately, my assessment of ME3 is that: it made things better, but not great and not fixed. And I hated James with a passion, the only ME character that I absolutely hated.
Looking at the ending of ME3, it looked a lot like they were aiming for the same sort of cinematic feel that DA:O had … and failed. And I think my admonishment of the entire series is that ultimately they tried to make things too cinematic and didn’t try hard enough to make it work as a game. I agree with Chuck at SFDebris that DA:O did make you feel like you personally were responsible for those forces, but it seemed more impersonal in ME3, despite it being because of you again, but I think that that was because those did fall more directly out of the game than they did in ME3. Ultimately, the demands of the cinematic experience limited the impact your choices could have on a large scale … in a game series that kept trying to pretend that you could control the fate of a galaxy.
How the choices impacted you personally and your companions personally was interesting and generally well done. How they impacted the galaxy was generally not so interesting or well done. If the series had focused more on the personal interactions of one crew that had an impact on the galaxy but was not critical to it, it would have done better. Unfortunately, it didn’t, and that is to its great detriment.
The overall impression of the series is this: it could have been a classic, but wasn’t. It’s a good series and I don’t regret playing it at all, and may even play it again … but KotOR is an overall better series and is definitely a classic, and Mass Effect isn’t. All of the elements were there, but they just couldn’t put it all together. We’ll see if they can learn from their mistakes with Andromeda.