I'm gonna make this review short so here is the positives and negatives for this game.
Positives
Subspace Emissary is awesome!!
Final Smash Balls are great finishing moves
more stages
Stage builder is an awesome feature
Online mode is great
More characters
The trophy collecting mini-game is fun
saving replays and sharing with friends is a good way to add replay-ability
Negatives
characters are nerfed (especially Mario, Peach and Meta Knight and they are my favorite characters!)
not much stage building items
Online lags at times