Well ME2 really didn't do much to further the overarching plot and it threw so many new characters at you that it couldn't properly develop any of them. Tell Garrus in ME to: stop playing by the book or rejoin C-Sec, it really doesn't matter. Destroy or preserve the Collector base, it really doesn't matter. Do either of these (and any other similar gripes) truly affect ME3? Maybe but when you stop to think about it, ME2 does sweet fuck all to advance the story despite it being a great game in and of itself. It's more so just a pit stop for Shepard to shoot at something different for a game.