Very fun. I play it from time to time and it seems to be the best way to play it (if you want to play more competitively). With friends in custom lobbies, it's endless fun. When you hit the ranked ladder, don't do it for too long or you'll tilt out of your mind, as you would in other competitive games.
There is no game out there as accessible and fun as Brawl for me, since you can boot it up in like 30 seconds and get in a match in 10. Plus, it's free.