Well, I have my likes and dislikes of it like many others.
My likes are how it's fast. I never cared for Brawl's speed, which is one reason I play Brawl+, I prefer playing SSB's in a faster, more aggressive environment, regardless of the level of "competitive depth"(especially because of how Berserker-esque I play.) I also love the return of L canceling. And the new ledge occupancy thing for tethers is genius! vBrawl should've had that ;__;
My dislikes are how the majority of the characters are handled, and I'll go into some depth with this.
There were a lot of character changes that I found interesting and liked a lot. Lucas is one that I think is fantastic, especially given how it changes him from Ness more by giving him a new, more useful Up B, among other things.
I like Ike's new tweaks as well, it gives him some improvements without completely changing a lot about him.
Then we have changes like Lucario. Lucario is one of my mains, and I personally didn't like the giant overhaul it got. I do like how the SideB has use in the air now(again, this should've had aerial use by default. C'mon, Sakurai : /), but everything else that was changed just seems too different now. It doesn't seem like the Lucario I've come to enjoy playing as. It's something that I feel a lot of PSA's succumb to - a moveset that just isn't very...Smash Brothers-y. But it is still an interesting idea nonetheless.
I find Wario is another example, but to a lesser degree. His changes make him reminiscent of his earlier days starting on the Gameboy with Wario Land, but I'm not too excited about the radical level of change. I'm not really one to believe in remaking a character from scratch for the sake of being competitive(although, de-cloning is still an idea I find appealing), but then again, I'm either the world's most competitive casual or the world's most casual competive player.
My idea would be to instead focus on improving what they have, as opposed to changing a bunch of things, or to keep the changes to a minimum, a la Lucas.
And I know this will seem like a minor nitpick, but given how I'm very anal retentive about all things about Marth/Roy(this may have been changed in the second demo. Haven't nabbed it yet) But some things with Marth that were not really changed from an aesthetic point of view.
Many of his animations were different in Melee, but I'll just bring up two attacks that looked different, with one of them moving in the opposite direction.
His 3rd down side B hit was not changed back to Melee's, nor was his fourth up hit. The 3rd down hit is less of a problem, but the 4th up it travels the other way now. This was not changed in this first demo, and it seems contradictory to say all his Melee hitboxes were restored when that attack goes in the opposite direction now.
Pic time!(Go! Go! 10 second doodle powers!)
And I find Velen brings up a good point about balance. Instead of bringing everyone up to the Fox/Falco/Marth/Shiek/etc range, I think it'd be good to have things a little lower. I recall reading that Pokemon Trainer(With all 3 mons together - not the "wild" ones) was cut for this reason - He just couldn't fit in the competitive level the others were able to.
I, personally, found Marth was pretty overpowered in Melee. Same goes for Falco. It felt like when I played as or against these two, it didn't require the effort/skill to be as good with them as it did when using a character cursed to be in the lower tiers, like Roy or either Link, or God forbid Bowser...And even then, with a low tier character, sometimes all the skill in the world will not save you... ;__;
I can understand the goal of P:M, but I think making everyone better/viable would be easier if the 'bar' weren't set as high as it is.
But, either way, I still did enjoy the first demo a lot, and I'm looking forward to what is to come. I hope to get my hands on that demo soon