here we go new info...
Super Smash Bros. Brawl will be fully compatible with the GameCube controller. Sakurai's reasoning is simple. He doesn't want to alienate gamers that prefer the traditional gamepad.
The game will feature online multiplayer. Single-player mode will see some changes, but Sakurai has declined to elaborate. Miyamoto did say (via translator) that we can expect "a very robust" single-player mode.
Super Smash Bros. Brawl revealed for Wii, featuring Solid Snake! [update] - Joystiq