Garrus is a BAMF, and so is Thane. Granted, I tend to choose my characters just by the way they look, and I was totally diggin' the fucked up armor and face in ME2. I picked Garrus in ME1 too, so that's another reason why I most likely liked him.
All of the characters that returned from ME1 got fleshed out even more, and I think some people got a tad blindsided by how they acted in ME2 (like Tali). I'm not sure if she is supposed to act more like she did in 1 or 2 really. I was more pissed with the fact that all of your favorite characters in ME2 could die because you picked them to go out at the wrong parts. Like I was supposed to remember who was the best at what (A load of my friend mocked me for not picking the right person to go into the air ducts, or whatever they were).
So by the time I got to the last boss, half of the characters I liked were dead I couldn't have given two fucks about the ending. They should have (IMO) made an intro story for all of them (which they did), and then made a sort of climax planet plot for each one, where after you had found everyone you could venture out to planets and you would have to make a choice and someone could die there, possibly saving someone else, or tying into their race cannon etc.
That would solve another problem I had with two, too. I hated how after I found everyone, the main plot was ready to go, right then. I could have done the side quests to earn each companions trust, but I didn't want to do all of them. I also got that each planet with a major side quest would be a new character plot point after about two of them, so it was really underwhelming. They really need to mix it up, and have the stories kinda blend so you are not quite sure who the plot point is really going to impact until you hit the end of the mini arc on the planet.
That and I want more weapons and armor dammit. I had a lot in ME1, but horrible item management. I got little in ME2. Fix yo shit.
EDIT: And half of the things seemed far too... random and fell into place. I mean, they even brought him back from the dead just to start the game off. It didn't seem to flow very naturally; or, it didn't seems very plausible that all those things would have happened. Far too "by chance" if you get the picture.