Seems like everybody only cares about which characters will be in the next iteration.
To be honest, once I begin actually playing a game, I don't really care what characters are in it (The obvious exception being falcon). I always just play the character that fits my style the most. Therefore, in SSB4, i just want deeper gameplay.
Here's the additions I want:
Wavedash
Yes. Wavedash. But not really the wavedash from melee. The wavedash in melee wasn't really intentional, and it forced you to practice technical skills for no real reason. What I'd do if I were in charge of the next smash game is, I'd add a dash, only possible to do on the ground. Basically a WD assigned to a button (say R on the GC controller). Possible to do forwards, backwards and while standing in place. Also since wavelanding on platforms was very tech-heavy in melee (i still can't do it), and you can't do it in the air, you'd be able to
buffer wavelands, making this difficult technique sufficiently easy for people growing up with brawl.
L-cancel
L-cancel should always be automatic, see brawl+ debates for arguments.
Dash-dancing
Like it was in 64 and melee.
(anti)Tripping
WHY SAKURAI?! WHYY!?!?!?
Srsly, if the choice were mine, I'd put in a 20-minute video of Sakurai apologizing for this and making penance for his foul deeds.
Melee 2.0
Not really, brawl did many things right. Brawls cast shows much more variety than melees, with characters like Snake and Olimar. Some of the characters are truly original, and I'd much rather have the characters from brawl (though rebalanced) than those of melee.
Combos
You can say what you want about Brawl, but combos are missed.
I'd however like to see more DI and patches removing all inescapables (including (only inescapable (and ******** (like D3s))) chain-throws).
Captain Falcon
God tier.
Balancing
Done through patches.
Patches done by this guy
(that's David Sirlin, for those of you who didn't know)
Basically kind of like melee, but without the tech skill (which was unnecessary, really).