Three comes into mind immediately:
1) final fantasy XV. This was another majorly hyped game, in the brewing for over a decade and failed to deliver up to expectation. The gameplay itself was fine, open world map what not and cool graphics, but the story is a major let down. I’ve seen the infamous 2013 trailers, of what was then final fantasy versus xiii - looked like a complete different game to be honest if not for the character design. Too bad we could only speculate what it could’ve been had tetsuya Nomura continued on the project. this one disappointed me the most, because I paid full price for the game on release day and it was a major let down.
I personally really like FFXV, but I will say that I didn't buy it at launch, when the game was still buggy and incomplete. It's pretty darn good now!
The only downsides now are 1) part of the story is told in other media (a movie, some anime, etc), and 2) there was some stuff that was planned to be put in the game as DLC but then Tabata left Square Enix. That story has been created as a novel, but it's just more other media shenanigans. The game is perfectly enjoyable without the other media, but there's pieces of the story that are harder to understand without it.
Personally, not sure if Nomura would've made it better. But I have strong opinions for Kingdom Hearts, feeling like that entire series is way overhyped, and think it might've been better without him.
Madden 10 Xbox 360 >_>
What are some games that you have regretted ever buying? One game I can think of that I regret getting was My Sims Kingdom, Mario Party DS, and the Cars (The Movie) game for the DS.