I basically second everything that's already been said, plus I'll add:
Smash Bros. is the only fighting game that's interesting to me anymore. Street Fighter 2 and the Mortal Kombat series perfected the 2D fighting game over a decade ago, and the 3D fighters like Tekken, Virtual Fighter, etc. have failed to live up to that standard. As Nintendo is known for doing, they basically overhauled the entire formula and reinvented fighting games. They created a fighting game with loads more content, lots of interesting gameplay modes, an interesting single player campaign that isn't just "kill this person, now kill the next person", and a kickass multiplayer game that allows up to 4 players. They kept the basic moves simple so that it's easy to play, but gave the characters hugely different moves leading to highly varied playing styles, and added items to keep things even more interesting. There's just no point in playing another fighter IMO.