How many topics are there going to be that ask this? How many times am I going to have to type "Secret of Mana"?
Come on. Three player support and real-time combat. Unbelievably good. I can't stand any RPG that makes you take turns. It's also nice when an RPG features multiplayer, though it gets to be really tedious trying to ensure that every player only uses their character to play with that one party so that everybody stays on the same level throughout the extremely lengthy adventure.
Aside from Secret of Mana, I must say Mass Effect is tops. KotOR is pretty much the same thing, so it too is indeed tops.
I kind of like Neverwinter Nights. I used to play Baldurs Gate but I didn't like it. Since Neverwinter Nights is similar, that's pretty much why I only "kind of" like Neverwinter Nights.
Fallout 3 is really cool, although co-op would have made it a lot better. Oblivion is garbage unless I get good mods for it.
Diablo 2 is incredible. Diablo 1 was cool when it was new but Diablo 2 makes Diablo 1 worthless. To me. Except for nostalgia.