Smash Bros as a multiplayer game is pretty great. As a singleplayer game, though...it's a little malnourished. Best way to fix that? Throw in a singleplayer, story-driven "side-scrolling action game":
...we've managed to create a complete side-scrolling action game. It's storyline isn't overwrought - it's hastened along by a bunch of quick movies.
The Adventure mode also emphasises character development. You'll see many famous characters persevering under the weight of their personal histories, shouldering their unique burdens... It's really something you won't see anywhere else.
Character development? Side-scrolling? Adventure? Character development? Hah! Alright, this should be...well, it'll be pretty interesting to see what they do with this, actually.
What is the Subspace Emissary? [Smash Bros Dojo]