OK, spent lots of time playing today. Let's be brief for each character.
Ike: quite slow. His fair is garbage. His final smash needs to hit someone next to you to activate. It's a guaranteed kill if they have medium damage.
Mario: d-air is tornado and I couldn't get it to rise, but I suck. Fludd attack is really wimpy. His final smash pushes you across the screen if you get caught in it (contrast with Samus').
Diddy Kong: weird movement. His b-air is like Mario's and chains together really well; I used it 4-5 times in a row to kill someone off the side of Castle.
Link: he's OK. His up+b doesn't seem to pseudo-spike if it hits after the initial strike. His bomb will kill someone in sudden death.
Sonic: has a really large dash dance.
Bowser: is pretty good. His final smash is amazing and is basically a free kill (at least). Fortress cancelling, fortress from shield, and flame cancelling are back.
DK: his back throw sends you down if you use it near the edge.
Samus: can't bomb jump in the air very easily, maybe not at all. Either the timing is significantly different and no one could figure it out, or you just can't do it at all. You can still bomb jump on the ground (the bomb will send you into morph ball state). Either can't missile cancel or the timing is different to make it difficult to test. Using a bomb in the air gives significant mobility though.
Peach: d-smash has shorter range and does less damage; I used it on HugS in sudden death and it didn't kill. Her dash attack is now two hits, neither or which is particularly powerful. She can still pull beam swords (I WAS THE FIRST PERSON TO EVER DO THIS IN BRAWL -- WRITE MY NAME DOWN.) Turnips have some variety but none of them approached the power of Melee Stichface. Her F-air is still good, and her b-air is stronger. Her final smash can be shielded -- HugS had his shield up when I did one once, and his shield kept flashing and getting smaller like he was shielding something (I also did NOT get any peaches from this attack -- may have been a bug). Using her FS when opponent is in the air appears to warp them to the ground, but this may have just been them falling normally while the animation was playing. I don't think she can float cancel anymore; I was never good at it in Melee, but I tried very hard to look for any sign of FC aerials and couldn't find anything. Her usmash shows a heart at the top of her hands. Daisy is still a costume for Peach. I played her quite a bit.
Pit: doesn't seem very good; couldn't find a decent kill move?
Metaknight: very fast and lots of combos; his side b does a lot of damage but leaves you helpless after it finishes. I don't think he has many kill moves either, because I almost always saw him killing people via items. FS must connect with opponent, then it's an auto kill (?).
Pikachu: is cool. He has some badass costumes. His uair and fair combo very nicely into each other. FS is very hard to control, but if you barely tilt the stick it's not that bad.
Techniques and misc stuff
NO:
Wavedash.
L-cancelling (MY PERSONAL THEORY: l-cancelling was made automatic for the demo, because there are clearly moves with much longer recovery times shown in some of the trailers).
Double jump cancelling (Peach/Yoshi).
Yoshi jumping out of shield.
Start as Zamus (couldn't find a button combo).
Light shield (classic controller shoulder buttons are not analog).
Cannot seem to short hop with the Wiimote on its side.
YES:
Dash Dance.
Teching (normal, wall, and wall jump).
DI.
Smash DI.
Chain grabbing (was CG'd by Pikachu's dthrow [without DIing it] and have heard that Mario can too).
Crouch cancel.
Grab items in the air with Z.
Air dodge grapple with Link/Samus.
MAYBE:
Wavelanding; some characters seem to do something like a waveland at times. Hard to test.
Jump cancel shine. Reports vary. Most people cannot get it to work, but some claim you have to hold B while you press jump for it to work; they claim releasing B makes him start a "turn off shine" animation.
COOL STUFF:
You will grab the edge during/after most moves even if you're facing the wrong way.
The Edge Hug: HugS discovered this. Walk off the edge and smash the stick towards the stage. You will grab the edge. Faster than WDing off to edge hog. This is called the Edge Hug, of course.
C-stick does tilt attacks if you also hold the regular stick in the same direction. This makes it very hard to CC downsmash with Peach, because holding down to CC and then C-sticking down will do a dtilt, not a dsmash. You can do all tilts using this method.
Fox can short hop triple laser. But his lasers do not go very far; they disappear after a distance that is about the length of the hole that appears in Bridge of Eldin.
The amount of action is crazy! It was kinda cool how they were on the Halberd, but then got blown away, it will likely be for a later part. 