I didn't buy many games, but the one I probably regret the most is Skyrim. Not because it was bad, but because I bought it on PS3, and I hated the controls.
Out of curiosity I just had a peek at the d3 forums; sure enough people are still complaining about it. People are writing 10 page stories detailing why they don't like the game. I would have thought that a massive patch would have been created by now to fix everything. (that's what I've been hoping for so that I could go back and play it again some time in the future)
I really would like a good d2 successor.
After d3 I don't plan on paying full price for a game ever again. (unless under extraordinary circumstances) I've been mopping up older games on steam sales that I've missed over the years this passed year. Now that I've purchased an xbox360 controller I've been having a good deal of fun with some console ports as well.
Sorry, this is OT, but since everyone else is talking about D3, here is my take.
I actually really like the game, especially since they added MP and Ubers. What's funny is when I go back and play through D2 (ran through it just a couple of weeks ago) I actually don't like it as much as I do D3. It feels slow and sluggish compared to D3 and the gameplay isn't as enjoyable as I remember it. I think a lot of people just remember a time when D2 was really the only game of it's type, and everyone was fine with grinding away over and over slowly moving to lvl 99. Now everyone expects much more out of their games, and if within 1 year everyone isn't in godly gear they just abandon it and go to another game. I think we are just spoiled now with so many choices. Back then, playing a game for more than 2 years straight didn't seem as uncommon (at least for me with D2).
Granted, I got D3 for free, but it's still the game I played the most in 2012.