Overwatch. Played the beta, and was generally unimpressed. Got the full game, and I haven't played it since before Ana came out. My friend loves it. I just dont understand.
Half Life 2. Everything about it is... ehhhhhh. Its brown and boring, and I just don't care. Its only real saving grace is the Gravity Gun, but you cant hold a game up solely based on a gimmick.
BioShock. Dont get me wrong, I like BioShock, and the whole Andrew Ryan thing towards the end was great, but the actual ending was crap, and it just took its time for the story to really get going. Also, having to swap between your gun and your plasmids was just cumbersome.
Anything by Bethesda. The worlds are huge, and that is pretty much all the games have going for them. They aren't particularly pretty, they aren't mechanically deep, the stories are pretty average at best, and there generally isn't really all that much to do. Theres only so many times that you can enter a cave and kill a group of bandits/ghouls/draugr/whatever, before it starts to become repetitive. The games are a great playground for modding, but the vanilla games themselves are just painfully average. I don't really understand how they've been heralded for so long.
Undertale. I dont think that this game is actually bad, per se, but its more that everyone has held the game up to be the best game ever 10/10 that it has just put me off it. At this point, I find the game to be kinda pretentious. I victim of its own success, I suppose.