SSBB is as good as it gets, and that's not from a fanboy...
Hopefully then, you'll trust that when I give Super Smash Bros Brawl a 10, it isn't because I have Marion tattooed on my bicep (or anywhere else for that matter).
I don't think there is any such thing as a "perfect game". It's like a perfect piece of art or a perfect song; they just don't exist. For me, a 10 game is one that helps justify the expense of buying the console. It's a game that, when the next generation of console comes around, makes you think twice before tossing your old hardware. For me, games like Final Fantasy VII, Halo, and Baldur's Gate fall soundly into this category.
SSBB belongs in this category. I am new to the series, so I can't say how it stacks up against its predecessors. On its own though, the game is brilliant.
At first I was a little disappointed by the lack of a comprehensive combo system, but over time I came to realize that SSBB isn't trying to be like Tekken or any of its ilk. The fact is, there is plenty of action in SSBB without a real combo system, and adding something like that to the game would have interfered with one of the game's main charms: that the characters feel a lot like they do in their assorted native environments. Mario controls a lot like he did in the SNES games. The same is true for Samus, Sonic, and the rest of the crowd. This is what really sells the game. It's amazing to see all these different characters from such a diverse background come together in one game in a way that really works well.
The "story mode" of the game, Subspace Emissary, is practically a game in itself, with fantastic production values and great level design. It does a fantastic job of getting you to play all the characters in the game in a way that makes sense, and really excels at building a story that involves them all in a way that makes sense. I have a few gripes about SSE (e.g. I didn't care for the auto-scrolling levels, and there is a lot of repetition), but as a standalone game, I'd probably have given it a 7 (it's also a little short to be a standalone). The fact that it's a side part of a bigger game is what makes it so amazing.
I do have a minor gripe with the soundtrack. The music is reminiscent of the games from which the characters were taken, but not quite to the part to make me feel nostalgic. I get that the designers were trying to give the old stuff a new feel, but with the vintage gameplay from the characters, I'd have rather had more traditional music.
The graphics in SSBB are some of the best I have seen on the Wii, although the engine kind of cheats with a rudimentary anti-aliasing that blurs the picture (although this can be turned off). To be fair though, graphics aren't the main selling point of the Wii, and asking a 480p picture to look great on a 55" HDTV isn't reasonable.
The Wii's motion sensing capabilities are pretty much non-existent in SSBB (other than shaking the remote for some attacks, which is off by default). I guess this makes sense since SSBB supports all kinds of controllers, but I wish I could use the remote to at least navigate the menus, which look like they were designed for it. Again, this is a pretty minor gripe.
All in all, I love SSBB and am glad I added it to my collection.