When Brawl came out, I loved it. I got used to the new gameplay and adapted, and I used to stubbornly cling to it over Melee since it was the brand new game in the franchise with new content. One of my friends was always reluctant to play and he preferred Melee, and he said that he felt I only liked Brawl more cause of the content. It wasn't until years later when I played Project M that I realized he was right. At first, I looked at Project M like, "Wooow, really, they're making like, Falco, and Ganondorf, all cloney again? Lame." But as I looked at gameplay, and I started playing Melee more at a friend's house, who only had a gamecube, I decided to give it a try. Holy crap. This is what Brawl should have been. Even though it's not done yet, I would have to say Project M may even be my favorite Smash "game". Combining Brawl's content with Melee's gameplay, I can only wait in anticipation when it is done.
Now then, my point in saying all this is that I realized that I prefer Melee's gameplay over Brawl's. The physics just, feel right. There's no frame delay. When you run and jump, your momentum is conserved. But what I mainly like over Melee over Brawl is the accessibility. Not only can you play casually and have fun with items, and crazy stages, you can also play fast-paced, kick ass, more serious matches with great combos and mindgames and all that great stuff. I acknowledge Brawl's gameplay is different, but I feel it is lacking. Silly matches with items are all fine and good, but more serious matches just seem like hit and run. You're floating all over the place, waiting for that last hit to KO, ha, but then it never seems to come cause the characters survive so long!
Project M is Melee 2.0. But they're not just copypasting Melee. It may PLAY like Melee yes, but the metagame is so different with all the new characters, and the changes to the old characters, and the different stages! Not to mention that it's more about taking the best components from the three Smash games.
MAIN POINT (TLDR): This is the sort of thing I want from Smash 4. A game not only the casual audience can enjoy with its ridiculousness, but also the more hardcore audience can enjoy with its deep gameplay. I honestly would be most satisfied with it playing like Melee, but seeing as how that is an impossibility, I'll stick with tweaking of Brawl's engine. Namely, more hitstun, characters not surviving till crazy percentages, less sluggishness...the good stuff.
So ends my wall of text.