I can't decide if the worst thing about Mass Effect 3 was the ending or the fact that you get ONE new playable character in the entire game, and he pretty much sucks. Garrus, Tali, Liara, and (for me) Ashley all came back, and EDI was never interesting enough to be made a fighting companion, so Vega is pretty much the only new storyline I get to experience, and why would I want to? I know Bioware said they thought there were too many squadmates in the second game, but that only resonated with me insomuch as the cool concept of Legion was around for five minutes before you had to make the final push.
I would have made ME2 the same way, but basically said, "We know you guys, by and large, won't be nearly as interested in using your saved games where people die as you will in using the game where you saved everyone, so we're just going to make ME3 so that everyone survived. That way we can put Thane, Mordin, Grunt, and all the rest in more meaningful roles than we could if we left the option of them being dead on the table." Seriously, I don't even know if you get replacements in your squad for Garrus and Tali if you let them die. Why would I not restart and try again on that one?