I haven't truly regretted any games I played, rather I have a couple of games that I regret that I bought them new.
Those would be Mass Effect 2 and Zelda: Ocarina of Time. I literally ran out of reasons to play either of those games less than 2 weeks after purchasing. Had I gotten them for $20 or less it would have been fine, but full price, they were complete wastes of money.
To expand on this I am shitty at action games. It usually takes me a while to beat even short games because I suck. Ocarina of Time is too easy, plain and simple. I breezed through the first time with no real problems and then beat it a 2nd time without even getting hit. Not just without a death, without ever being touched. I didn't even bother trying to upgrade anything because I didn't bloody need to. I mean, after you do that, what more can you do with a game?
Mass Effect 2 was a blast the first time through, but after you've seen the whole story it just because a really long FPS with no compelling reason to play that many freakin missions. Neither the story nor gameplay vary enough to make me want to keep going more then one mission at a time. It sucks because BioWare keeps coming out with new DLC for a game that I have lost pretty much all interest in. If I had waited to buy it, I could have had a blast playing the complete package. Instead I'm going to have to trudge through a bunch of boring bits just so I can have a more complete gamesave for ME3. True you can play the DLC with an already ended game, but if it's anything like Dragon Age, it works a lot better when it's done with a new game file.