MGS4, the (numbered) follow up to my favorite game of all-time, and was going to be the stories end, I was so hyped throughout the games marketing, watching and reading everything about it, that it put me off getting really hyped for anything ever again, although I still really liked MGS4, it just end up disappointing if you get too hyped for a game.
Though Kojima still got me pretty good with MGS5 too, those pre-release trailers were too damn good for me not to get a little bit hyped, that also disappointed though