What game was it and do you regret buying that game?

Call of Duty (not to bash the series) 

Max Payne 3

Borderland 3

and there were a few more, but I can't seem to remember at the moment.

Pokemon X.

But I really don't regret it. I still need to go through Victory Road and beat the Elite 4, but so far it's a really fun game. But it's not something I would call amazing.

Heroes of Ruin for Nintendo 3DS. It was from SE and was meant to be a handheld Diablo.

Project X Zone
Cod mw3
Bf 3

Borderlands... A friend of mine hyped it a LOT and it kinda stuck on me. I bought Borderlands 1 and 2... I regret that decision to this day...

Demon's souls... i know shocking but i couldn't pass the 2nd boss since the game was extremely difficult and at that time i was discovering the genres for games and knew by then that RPG wasn't for me.

Call of Duty MW2-BLOPS(not getting Ghosts)
GTA IV
Devil may Cry 4
Infamous(though this turned out to be a good thing)
Uncharted 2(again..turned out to be a good thing)

Batman:AC (worth it)
L.A. Noire (Kinda worth it)
Crysis 2 (Regret paying full price)
Crackdown 2 (Regret paying full price)
Assassin's Creed 1 (Kinda Worth it)
Rise of Nightmares (No comment)

The new Sim City. And Yes, I REGRET buying it. Worst purchase in years!!!

Metal Gear Solid IV - Worth it
Metroid Other M - Last time I bought a game based on hype