Nice break from everything else. Must own title.
SSBB is an overall great game. After shooting terrorist and chopping zombies for months, this is a great break.
Single Player: Good. Not great, not bad, but good. The SSE is an awesome way to bring single player to the Smash Bros. series. My only problem would be the lack of depth. While it is very fun, it's not near as fun as many other single player games.
Multiplayer: Almost flawless. There's nothing bad to say about the Brawls, they're perfect. The variety and fun factor is jarring. Co-op is a bloody good time too. My only complaint would be with the online service as a whole. You play random people one time, don't talk to them, and then never see them again. Nintendo Wifi has a lot of work to do to catch up to Xbox Live.
Overall: Must own for any Wii owner. I may have put in a lot of negatives, but that's because everything else is just perfect.