Assassin's Creed III is the best example I can think of. I love the series and Revelations is one of my favorite games ever. Then Assassin's Creed III launches as full of bugs, boring missions, and characters I don't care about. It was the first game in the series I felt wasted its setting. Also, the new controls were bad, sapping the fun out of the core, fun free-running mechanic because maneuvering around was so awkward.
In the end though, even patching the bugs didn't fix the poor mission design and bad story.
Another one is Hell Yeah! Wrath of the Dead Rabbit. I wasn't anticipating this game for a long time or anything, but the trailers were so endearing that I found myself looking forward to it. It had a fantastic soundtrack and some fun, goofy humor but the game kept getting worse and worse as it went on. There's too many spots of poor game balance: enemies breaking the rules of the game by attacking you through walls, repetitive boss fights, and badly spaced checkpoints. I started off the game having fun, but around level 3 it started going downhill and I left disappointed. Awesome style in that game, but it's not a good game.
@historyinrust: Ah, I didn't know about the stuff that was added in patches. I didn't get into the game until around the Ultimate Edition because it seemed to have a lot of issues. I recall EVO 2013 being boring because of the low character variety (Superman players dominating, basically)
But now that the game has been updated a lot, it's a lot more balanced and more fun to play AND watch.
I am absolutely appalling at fighting games usually. But this is the first one since Tekken 2 where I feel like I, as an absolute beginner, am capable of stringing together more than just singular punches and kicks and for that reason I'm really enjoying it.
I've even ventured online at one point and didn't have my arse handed to me within 15 seconds.
Yeah, I was actually winning matches shortly after getting online. It's a pretty great encouragement to keep going.