I <3 my Wii.
SSBB is by and large more fun than Halo could ever hope to be in my eyes.
But this is my personal opinion and I'm sure MANY will disagree, but meh..
I was never much of an FPS fan, I mean to me they're all clones of DOOM (with interchangeable WW2 or Sci-Fi plots) which in turn is a clone of wolfenstein 3d.
Brawl adds something new to the mix. An online fighter with a more platforming element to it than the standard arena fighters. Also it incorporates online "death matching" into the mix, all whilst using lovable gaming mascots we all grew up with to kick the ever loving hell out of each other.
There is right now the biggest reason to love your wii: Super Smash Bros. Brawl