Dr. Mario. No change I can think of.
Mario. I can't really think of any changes either. I would like to see him use the hammers from his RPGs though. And alter Mario Tornado with him having the cape on, just for that nostalgic feel. :D
Luigi. Lose the Luigi Missle, please. Give him better recovery and I'd like him to have some thunder abilities like in Superstar Saga. Nothing over the top, but it'd be nice, all I'd really like is better recovery.
Bowser. Make him literally heavy, but not Metal Box heavy, just where he can't be offed the stage so easily, that super armor idea BPS suggested sounds good to me, and speed him up some. And perhaps another projectile, I dunno it seems more Bowser-like if he was throwing hammers or spiked balls or something. XD
Peach. I'd like her to be updated to fit her Super Princess Peach abilities.
Yoshi. I can't think of a **** thing...
DK. Same with Yoshi. I can't think of a way to improve him.
Captain Falcon. I still like his u-smash from SSB64 better, but other than that he's fine.
Ganondorf. I'm torn. I really don't want to see him changed save for a few tweaks, on the other hand I want him to be his own character. I particularly like his WW version, two swords and all that. He wasn't the prettiest fellow but he was also badass in his own right.
Falco. I can't really think of anything besides bettering his recovery. I'd like to see him with a new movelist but I wouldn't know what to suggest.
Fox. I really don't know, I really don't like Fox and I'm sick of playing against him. I probably wouldn't mind if it was his Starfox Adventures version.
Ness. I'd like him to be more like his SSB64 version if not just like it. In today's metagame he wouldn't be so overpowered. Or at the very least, fix the yo-yos.
Kirby. Lose those weird sweet spots, a better dash attack, much like his SSB64 one, make his throws more useful. Give him the full cutter combo already, and it'd be nice if he could combine powers like he could in Kirby 64, though I wouldn't know how to make that work.
Ice Climbers. Can't think of anything.
Samus. Honestly she's fine the way it is. but I'd like to see more of her other beams as seen in Prime 1 and 2.
Zelda. She's fine to me.
Shiek. Stop her chain grabbing ability and what the heck is up with that whip?
Link. Really he's fine in my opinion, if anything, just fix his recovery just a little.
Y.Link. Redo him completely. Link and Young Link are different enough...just keep the boomerang. ^^
Pichu. More range, different moves.
Pikachu. Needs more range, then he's fine. Oh and fix his f-air to be useful.
Jigglypuff. Only thing I can think of is better ground ability, but honestly, he's fine as is.
Mewtwo. Come on, he's freaking Mewtwo! Why the hell is he so horrible? He's supposed to be far heavier and much more powerful. Just enough where he'd fit to the top of mid tier anyway.
Game & Watch. Really he's fine in my opinion.
Marth. Fine as is.
Roy. I'd like to see him differen't but I can't think of anything.