All of you people who clearly don't know what smash is, watch this trailer before typing anything else.. it will show you just how different it is from other fighting games, and just how many features it has (to those who know what smash is, also check it out - no spoilers)
http://videogames.yahoo.com/events/super-smash-bros-brawl/super-smash-bros-brawl-video-premiere/1186004
EDIT: if it shows a bit pixelated, refresh the page - i'm not sure why it does that, but it should be clear - stupid yahoo videos