KotOR II was awesome, and I was satisfied with its ending (oh yes, I said it). Can't judge ME3's ending, but even if it is that bad, I think there are quite a few endings in gaming history that are worse. From the choices given, I picked Neverwinter Nights 2. Gotta be honest, haven't played half of the games on this list, but you can't deny the cheap ending to an otherwise decent game. I think I would've included Dragon Age 2's ending as well, then again, maybe it doesn't deserve to be named among these otherwise great games.
Also, mim, we need a "best ending to a video game" next.