Yay demo! Link feels much, much, much, much, much, much, *repeats much 50 more times* better than in any SSB games I have played - I never played Project M before. Holy crap is he fast, fluid, and powerful compared to the past incarnations. He is truly worthy of the title of: Hero of er... Smash? Zelda? Links? Whatever, Link's good. Also, jump attack is awesome, but risky if you screw up your distance - you'll just jump right over. I will definitely play as Link as a fighter now than for nostalgia.
Mario feels really off. I was never a Mario player, but I do play Luigi a lot and I'd say they're similar enough where you can have some skill in either character. Maybe it's spacing issues, unfamiliarity with the 3DS's layout - B and A are "switched" compared to most layouts - or something. I can't pick up and play as him like I did with Pikachu, Link, and Mega Man.
Speaking of the mega man, he feels great and unique. Mega Man's style is much more different than any other character I have played as. Since his neutral A, side-tilt, and nair are just pellet shots - I don't know the official name -, he lacks that oomf or regular combo feel like everyone else, but that gives him more range. Also, his side smash is out of this world! My go-to kill move right there. It's also fun having personal sticky bombs and using the Shoryuken. I might not use him often, but he's a breath of fresh air.
Pikachu has new animations and they're sorta cute. Play style seems familiar as far as I can remember, but I really need to work my distance and combo-ing skills. I'm more used to rush-down characters, characters who have "moving" attacks like Fox's side smash or Snake's dash attack, or Ike's sword distance - maybe that's why I'm having trouble with Mario.
Haven't played as the Villager yet. Probably won't for some reason. It's their eyes, I tell you! Murderous eyes that stare into your soul.
I wished there were more characters to choose. Why not have Samus, Kirby, and Fox too? Whatever, just 2 more weeks.