You people don't understand. You would rate 10 to anything that you like.
10 means that is is perfect, nothing can be added, it is at it's maximum.
SSBB is a great game, I love it, but it can improved in many ways, and it's not at it's maximum. That is fair score and I would of rated it the same.
IGN rated it 9.5 too. Here is what I think can be done to make it a 10.
-SSBB has great graphics, but not the greatest, they could if they really wanted to, make the graphics higher.
-Online Brawl Rankings. Not many people care about this, but it would make the game more amazing.
-Voice Chat. Not necessary, many people don't care, but if you want a 10/10 on a game you have to go the extra mile.
There are also little itsy bitsy faults that are not worth mentioning, but other than that this game is great, but does not deserve 10/10, so please leave it to the profesionnals. I'm not trying to be mean or an a** hole, just saying, so please don't take it the wrong way, SSBB is a great game.