There are a few games I've gone back and played on the ps2/1.
SotC-still awesome FF9- still awesome We Love katamari-best in the series. Baldurs Gate Dark Alliance- still fun
There are a few more I can't think of. They're all still great games, but I still feel like games from this gen are just better.
Edit: Twisted Metal 2. Better than tm black. I'm still waiting to get the new one at a decent price but I don't see it being much better than 2. Other than some wonky driving controls, it has everything. Fun local mp, great levels, cool characters with interesting back stories, neat weapons, awesome fast paced action, secret unlockables(mother effing Minion!).