Assassin's Creed Odyssey
Well, I was quite enjoying it until the end, which is ridiculously anticlimactic and just made the whole game feel like it fell flat. The end was so much not an ending that I didn't even realize it was the end until the achievement popped. Like, seriously, I felt like I was getting kind of close to the end, and that this was just a little lull before the final climax. Your game should not end on what feels like a lull...
*Edit - I mean Jesus, it was just bad...