Actually, based on what I've read about the IGN podcast, is that they don't think Super Smash Bros. Brawl isn't a bad game at all. Only Subspace Emissary didn't live up to its expectations.
They never stated the rest was lame, in fact, they liked the rest. They think Super Smash Bros. Brawl stands well alone as a multi-player game. However, if the adventure mode was more solid, Brawl could have reached those doubting Brawl.
Smash has always been a multi-player game. They acknowledge that, however, they also take into account that Sakurai had put more effort in making the single player as appealing, so that's how Brawl gets its critique. It's not that Brawl's a bad game, it's because Subspace Emissary is rather disappointing.
Sakurai himself said he wanted to put more emphasis on the single player aspect, however, the IGN employees feel like it really doesn't show.
I'm going to listen to the podcast now. If I come to the conclusion that IGN has been right, then it's pretty much over with you guys. I'm kind of sick of this fanboy crap.