Personally there are a few games which left me very dissappointed, after hyping myself up for years in certain cases.
Divinity Original Sin: turns out I prefer more streamlined, less packed games (love Pillars of Eternity) and that coop play in a CRPG stresses me out.
Wasteland 2: I actually managed to finish this one but secretly I admit I was hoping for a better Fallout which I didn’t really get. New Vegas did the cowboy theme much better.
INSIDE: while the design was cool, it was just a ton of boring, easy puzzles in comparison to LIMBO, its predecessor.
The Legend of Zelda: Twilight Princess. It was so tedious to get through the opening area that by the time I got to the first dungeon I was getting tired of it. It did get better after that dungeon and the game opened up a lot more, but it one of my least favorite Zelda games.