This is going to make me unpopular (who am I kidding? It's going to make me more unpopular) but I don't think the Smash Bros games are all that. The fan service is fun, but I'm not really a fan of the gameplay or mechanics (unsurprising really given my dislike of Kirby platformers).
I had pinned quite alot of my hopes for Brawl upon the Sub-Space Emissary, and while the connective tissue of that mode (i.e. the cutscenes) was pretty cool, the gameplay just wasn't there for me.
As I don't have that many people around me who would be willing to play video games competitively, I was also looking forward to playing online. I think we all know how that went.
Largely because of the terrible online and the really boring adventure mode I didn't have all that much to do apart from unlock things.
I can appreciate why it's this high up this list (clearly lots of people enjoy these games), but to be honest it probably wouldn't crack my top 20 never mind my top 10.