Excellent. Extremely addicting and fun.
Gameplay: Some of the best I've seen in a fighting game. Every character has their unique style of fighting, unique moves, unique everything. The game runs at a really nice framerate and everything is very smooth so it feels great.
Graphics: Probably some of the best on the Wii. The hardware can't push very realistic graphics, but what was done in Super Mario Galaxy and Smash Bros is still quite amazing, nonetheless. It looks beautiful, the colors are striking, the characters are detailed, and the level design is magnificent. Some very trippy visuals in this game, believe me. Sometimes, I wanna stop playing just to enjoy the craziness that's happening in the background.
Storyline: Nothing special, really, but a pretty cool co-op mode. Just your basic evil invaders, where you have to take them out by playing different characters that are introduced along the way. Also, you can play the other single player modes like classic mode, or All-Star mode, which are pretty cool too.
Overall Value: Totally worth it. It is an extremely addicting and fun game to play by yourself, with your friends, or online against a random opponent. There's tons of strategy involved to make it competitive, and loads of wacky items to fight with to make it insanely fun. If you've got the cash, go get it because it's probably the number one reason to have/buy a Wii right now, in my opinion.
There's my two cents.