I'm about to sound like I'm not a very "hardcore" gamer, but Kingdom Hearts is probably my favorite game of all time. It has to be, because I've beaten it 100% well over fifteen times, and that's just in the last four years.
Diablo 2 was a lot of fun. I like Torchlight also. And holy ducks, pokemon. I've put a lot of time into that too, haha. My favorite pokemon was probably silver; when they remade it recently I put in a good 100 hours at least.