To hell with adventure mode, and any other single player aspects of SSBB.
SSBB is Nintendo's flagship
MULTIPLAYER game.
If they botch yet another SSB game with clones and cut corners because they spend too much time focusing on the single player instead of the multiplayer, then I will eat all of Sakurai's children, starting with the most tender and moving to the stringiest.
Let me further illustrate this point with a graph for better effectiveness...
No one is going to buy SSBB for the single player, and even if you do, guess what? You will be able to play it ONLINE so you will still enjoy more multiplayer aspects of it because, no matter HOW much they focus on the single player, it will not be played anywhere near as long as the multiplayer, period.
So, bottom line: if you want to play Metroid, SMB or Zelda, go play that and let SSB be SSB.