Seriously the best game on the Wii, you need this game.
It is easiest to start off with the cons since those are so few so here they are. No online voice chat, despite the fact many people find there is little lag, I find it can become unbearable at times even though its mostly alright, Subspace can feel too long and you just want to get it over with, they made Link much worse of a pick IMO. (Thats a personal con) YOU'LL WANT EVEN MORE CHARACTERS WHEN YOU'RE DONE GETTING THEM ALL BECAUSE YOU CAN NEVER BE SATISFIED. And those are the cons, nothing too huge to change your mind about this game, just a few things that could have been improved upon.
And now the good stuff. Great roster to choose from, you can create your own stages, graphics are amazing considering it IS the Wii, online play, wonderful replay value, you can take snapshots at any time and save replay data to send it to your friends, many single player modes are made co-op. BEST GAME FOR WII.
I would actually give this game a 9.9/10 since there are those minor things that could have been improved on and it IS a sequel. But since I kind of can't do that I'll rate it 10/10.
And those are the facts, this game is over hyped but it is definitely worth the wait and worth the money. It will be played for years to come and if you don't have a wii you should seriously consider getting one for this game. It's just that awesome.