On one hand, Sonic Adventure DX is my favorite 3D sonic game, and I haven't played it in years. On the other, Megaman 64 haunted my childhood because I couldn't beat the first boss, and is on my list of childhood games to beat. Tough choice D:
It gets so much better, you get to create all sorts of new blasters, and armor and shit. There's also a Karma system which is pretty cool. Pretty big game as far as the map goes too.