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.
Having just played through the MCC recently the first halo is a bit dated, but 2 and 3 are some great campaigns. Reach and odst have decent stories, but the campaign is more average. The biggest surprise to me was how much worse 4 is than I remember. I knew it was disappointing, but playing it back to back with the others really makes it obvious.
I had played all the games before though.