We finally unlocked all of the characters in the game. The last one was Wolf, picked up in a stage redo in The Subspace Emissary adventure mode. He's a fantastic fighter, very quick and hits hard. Greg used him to great advantage. Along with the last character unlocked there are several other game types and events that become available.
I'd love to post some screens of Wolf and new stages, but my SD card crapped out. Lost the replays that I had on there and can't transfer any new ones. I should pick another one up this weekend to replace the busted one.