Although I liked the Pokemon GC games, I think SSBM, RE4, and LoZ: Wind Waker are better, I like each of them in different ways. Although these favorites will change once TP is out, or that will be my favorite Wii games. Another game that seems will be good is the Kirby game, that has yet to get a real name.
I have loved Sonic Adventure 2: Battle ever since it come out on the GC. It still remains my favorite game period. And of course using a disk that has the words 'replay' and 'action' on it enhances that game and mkes it even more fun!
For multiplayer, SSBM all the way. 'Nuff said, everyone knows why!