I have found that there aren't too many games I regret buying, I think I have regreted many more book purchases than games, and it is mainly because in general Video games have such great reviews. What I mean by this is with things like metacritic, youtube, and friends who buy the games it is reasonably reliable for me to know enough about a game to know if I would enjoy it or not (whereas with books the reviews seem pretty inconsistant, and lots of times reading the back of the book or rather the Amazon description is all you have).
That isn't to say I never regretted buying any. I sorta regretted buying Elder Scrolls V: Skyrim Hearthfire, mainly due to the fact that it was basically a package of things that mods already did, and jumping thru the hoops to build your house was a bit of a needless grind of gathering materials, Dawnguard was awesome, but I am indifferent to Dragonborn, even though i did pay for it.
Whatever games I buy, I get very cheaply, lots of games from 2010-2011 are $5-$10 on steam sales and will run at max settings on my cheap hardware (Asus G75vx, and A10/R7 260x powered desktop). I would never spend much on games mainly due to needing money for transition.