Garrus is definitely my favorite character out of all three games, and Thane was one of my two favorite characters in the second game. They’re both total badasses, but they’re also very complex, compelling, deep characters. The notion of Garrus as an almost ‘rogue Turian’ who does what’s right rather than what’s expected makes him very appealing, I think, because turians in general tend to be hard for players to relate to because they’re so rigid. And I think the dichotomy of Thane as a very spiritual man whose job it is to kill was fascinating; particularly the way he thinks about what he does (his spirit being independent and his body, which does the killing, as nothing more than a tool).
I also loved Mordin as a character. I know he’s controversial to alot of people because of his outlook on science, medicine, and the genophage; personally I thought that added alot of realism to him as a person. The whole genophage issue and his attitude towards it just really made me think about it from all angles, and realize that it’s not a simple, black-and-white, one-sided issue. And he IS conflicted about it and has alot of trouble dealing with it, even though he believes that it was justified; the beauty of the type of game that Mass Effect 2 is is that it lets you decide to call him on it or agree with it while at the same time learning about it and understanding it.