Most broken was probably Messiah. I have never had that game run on any of the four machines I have owned since I bought it. Even the GOG version, which ostensibly is supposed to work on newer versions of windows, doesn't really play. I got farther in that one that any of the previous iterations I had tried. It even loaded a level! Then the sound went out... my textures dissolved, my cat died, and my machine crashed.
Sword of the Star 2 was also a major big-riddled mess. I felt genuinely bad for the dev team. I have NO idea what happened, but they seemed as perplexed as their customers. As far as I know, they are still trying to fix it, but the damage is done. People care far too much about review scores to let a 42 Metacritic score slide, and to be fair, the state the game launched in didn't deserve HALF of that score.
And finally, I know it's pretty much rote by now, but Skyrim is/was one broken-ass game. It hasn't crashed on me since the patch a couple weeks ago, but it got to the point where I was crashing on pretty much 1 out of every 3 area transitions, and then just randomly every five minutes or so. No good.