I know this is late, but I had to respond to this. Mass Effect 2's plot was pretty thin, but it was pretty good when you realize the focus is on building a team. What's the point in building up all these characters just for them to get 1-2 short appearances and 1 mission in ME3? A few of those missions were important (like legion, mordin, and tali's loyalty missions), but that's just a few out of many. Aside from generic sidequests, the game consists of 6 "main story" missions, 7 recruitment missions, and 12 loyalty missions. About three quarters of the game is based on this team. You helped your team deal with their problems...just for them to do their own thing in ME3? I agree some could have important roles, but some of them don't join you against all reason.
One mistake many people seem to make is if a character has something important to do at one time, it means they can't be a squadmate period. Legion? He has to deal with the geth/quarian conflict! Mordin? He's got to deal with the genophage! People don't seem to realize these conflicts will have to be resolved at some point, and then why don't they join you after? Even further, the justification goes out the window when you realize how some of the shepard's actual team have incredibly important responsibilities. Why do people expect Legion, a geth of all things, to be physically present with other geth to lead them, and yet Tali is an admiral and she joins your squad just for the fun of it ?
I just have a bad feeling this thread , shortly after ME3's release, will have a bunch of posts asking "Is my favorite character on the squad?", and quite a large number of the responses will have to be "We have some bad news for you..."
Actually that's going to be all the responses. garrasu and talisu are there because the fans quite literally demanded it in gigantic numbers, Liara is there because she's Casey's favorite, Virmire is there through plot device and the other three are based directly on marketing concerns and the need for a "twist". The last of those is pure unadulterated fanwank. (and no, I'm not talking about Vega)