Some general impressions since I started playing with friends. We played for a while but not for days. Only like 3-4 hours. I had practiced a bit before hand so I would say I have 5 hours of experience.
General: Some Melee purists had nitpicky problems. Falls too fast,L-cancelling isn't perfect, grabbing on backwards. Many of them still seemed to have fun but would still complain after losing. You won't make these people happy, they want to hate this game.
As a smash bros fan people loved this mod. It takes all the great of Melee, adds a dash of the good things from Brawl (not braindead edge hogging, backwards grabs on recoveries, RARing, easier DI, etc) and combines it with some of the best lessons and codes from Brawl+. The buffer code is still in and a very, very welcome addition. Very polished and very fun.
Mario: Well liked though no one mained him in Melee, Brawl, or Brawl+. I played him a decent amount and he seemed really powerful, easy to combo with, good gimping game, and a strong kill game. One of Project M's shining, perfect characters.
Link: A number of Link mains were big fans of him. He feels exactly like Melee Link, just actually good. The arrow gimps are epic against spacies. Another great character.
Fox: Haters gonna hate. Anyone who played Fox in Melee should love this one. People mentioned he might fall a little faster but I was watching people do the same Melee tricks as before.
Falco: No one really tried him. He got one match against Marth in the Mario 64 Metal stage, got rolled because Marth was wavedashing halfway across the stage and no one touched him.
Jigglypuff: Same nonsense from Melee. For fans she will be liked, for everyone else, we just sigh and grin and bear it.
Marth: A personal Melee favorite of mine and he felt great too. The powerful Brawl DI makes some of his combos easier to escape, but that's a good thing in my book.
Captain Falcon: A perfect Melee transition. I wish the up-taunt easter egg wasn't so tough to do.
Ganondorf: Many agreed and seemed to think he was the best character in the demo. Both from sheer fun factor and overall presence on the battlefield. He was heavy, not terribly slow, devastating hits and combos, and it seemed much easier to Down-b gimp then ever before. I'd hardly call him overpowered, we didn't play a ton, but he did make strong initial impressions. Are his L-cancel frames the same? What I mean is he seemed to have little to no lag on L-cancels.
Game and Watch: Played like Melee but he seemed to die way too early. Another unpopular character who got limited play time.
Sheik: More melee greatness but people liked Zelda more.
Sonic: Seemed really good but no one could consistently kill with him. Any tips?
Lucas: Another really fun character and the new B attack adds depth to his game. SH-Nair is so good.
Snake: Seemed really interesting but once you got inside he just kinda flopped. Fast characters seem way too strong against him. I think a lot more practice will be needed to get good with him.
Zelda: Crowd favorite and a big surprise. Tons of cool tech tricks, the side b is crazy cool. Seems like there is a ton of depth to the character. My only complaint could be that having two characters in one is a pretty potent strength, but that's hardly a big one.
Overall keep up the good work. It's too bad that according to what I'm hearing it's gonna take a long time to see any new characters which is really sad and seems like a big waste, but I'm not the boss. If it indeeds takes forever to see more characters I'm sure many of us will fall off of Project M again.
Adding more characters keeps hype built for the game and keeps it feeling fresh and fun. Adding more characters doesn't make it like Brawl+ if the Dev team sticks to their guns. It also allows for any possible unnoticed bugs to get found or possibly game breaking things. As I said, many of us loved the demo and want more. I'm sure we'll play it for a while and then fall off the scene again till more characters come out. Keep up the good work and I really hope you guys consider releasing more characters or maybe character packs of 3-4 of them before we go into a final beta or just final release.
