1) The need to use the service known to mankind as Origin, the dreaded Steam-wannabe that fails at just about everything.
2) The counter-intuitiveness of said service. Not only have I been forced to download Mass Effect 2 more than once (I am on my third try), but I have also been forced to uninstall stupid Origin--but not so I can get rid of it--just so I can re-download the damnable installer again.
3) Did I mention, Origin, that Steam has never given me any fucking download problems? Tell me right now why I shouldn't bloody well pirate this game when I own it on my console and on the PC, hmm?
4) The fact that I need to play Multiplayer mode in Mass Effect 3 just so I can get the maximum War Readiness crapola. I would really rather not game with strangers. Kthx.
5) The Mass Effect 3 ending. Not so much because the ending was sad and Shepard could possibly die, etc, etc. The reason why I am angry about the ending is because I am following some really good Mass Effect fanfic writers out there, and some of them feel discouraged to write more now that the ending has reared its ugly head for all to see. Thanks for ruining it for them.
Honourable mention: The default choices that you get when you play without an ME2 import. Just be glad my friend is forgiving despite the fact that she has gone through the trauma of seeing Eve die because default settings say, "You did not let Mordin keep Genophage cure files" or when both the geth and the quarian attacked each other despite her choice to let both live because a) Legion isn't there, and b) apparently, the quarians will attack the geth anyway. Thanks a lot. Apparently, being a Paragon isn't really a good thing if you don't have the history to back it up.