I played for like an hour and I love it except for the controls...I hope you can change them on the final release, especially the L and R. Aside from that it was weird playing Smash on a small screen (especially since I have the old 3DS) but I got used to it.
For the 5 characters you can play as they all seem pretty balanced, Mega Man is probably the most "OP" one, and maybe Villager which can basically recover from anything (with side B and up B).
Nintendo and PC gamer