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.
I recently replayed that game after 10+ years. I think I could count the number of difficult jumps that required more than two attempts on one hand. The game is like $1-2 on a sale and you can beat it in 3 or 4 hours. I thought it was fun, but I could see how it would be disappointing if your expectations were higher than minimal.
Mirror’s Edge: Catalyst was much better IMO. Actual story. Decent characters. Free roam. Side quests.