I have a bunch of favorite games.
Top 5 rated list
-World of Warcraft Private Server
-War Rock (Everyone gotta love that)
-Ragnarok Online Private Server
-Phun (It's like the best 2D physics game ever)
I would really recommend them. I'm currently playing both War Rock and Last Chaos. On Ragnarok Online, there is basically nothing to do and Phun is fun but I can't think of anything to build. World of Warcraft, same with every other game that I'm not playing, nothing to do.
War Rock is like a war game. And Last Chaos is a Role-Playing Game. Google them if you want to play it.