I've had a few regrets of my own here.
One of my biggest regrets is snagging Sonic Riders. I'm perfectly aware the game has a lot of fans who will defend it, but unfortunately, I'm not one of them. In fact, I'm probably one of those people they'd defend the game from.
In fact, I consider it one of the worst games I had the misfortune of playing. And there's one reasons for that; the controls. I never got used to the controls no matter how hard I tried. All I got used to was slamming into walls and losing constantly. It didn't help that the levels and mechanics didn't feel like they were designed with this control scheme in mind. And sadly, the game's later stages are brutal in its difficulty even on the easiest difficulty; you made one mistake, maybe two or three if the game was feeling generous, and you pretty much lost the race. I know this, because I actually tried to see if I could lower the difficulty, and sadly, it was already as low as it could be.
In the off-chance I did win a race, I never felt like I won because of my own skill. I won because I got lucky. I'm not the most competitive sort, but honestly, if I have to win just to get to the next level, I'd really appreciate it if I didn't have to get lucky just to get to the next stage. And I'd appreciate it if my satisfication didn't amount to "thank goodness it's finally over!"
What makes it worse for me was that it had a lot going for it; the graphics were really good for the PS2, the story wasn't bad, heck, I even welcomed the Babylon Rogues with open arms. But the gameplay ruined the whole package for me, which is a shame, for that is one of the most important aspects of any game.
Wow, did I vent. But here's another regret: backing Mighty No. 9. I only backed $5 to the game, but I couldn't give much more then. But that turned out to be $5 more than the game deserved. I wish I never backed the game, and to this day, I have yet to back another Kickstarter.
And going back on Sonic; the 3DS version of Sonic Lost World. Now, let me make it clear; I enjoyed the Wii U version, warts and all. I enjoyed the 3DS version of Sonic Generations. But this version of Lost World dropped the ball hard. Basically, it takes the Wii U version's flaws and expands on them to unforgiveable levels. It practically made the game unplayable to me. A shame, since the first world actually is a good start, but the second world in, there's a huge difficulty spike.
I'm sure there's more here, but those are what popped into my mind.