I like Project:M, don't get me wrong, and I play it often. But there are two main things that bother me.
1. Everything from Melee feels clunky. I can go straight from Melee to P:M, and my Marth and Falco and Fox will mess up techs that I was just doing perfectly in Melee. I notice it most with Falco and Marth. It's weird, Falco feels so slow in P:M, like he's weighted down with something, and he just feels so goshdarn CLUNKY.
2. I don't particularly like the way that every new addition to the Melee roster has become a gimmicky character. By this, I mean that each character has an obnoxious strategy that is over-centralizing to his gameplay. Examples:
Lucario's OHC system
ZSS Stun Gun and tether recovery
Rob's side-b air movement shenanigans
Squirtle's Shell Shifting
Diddy's Bananas
Ivysaur's....everything His g*****n vertical chasing seed thing and his f***ing shield-eating Razor leaf not to mention his easy as all hell recovery, talk about taking skill out of the game
Snake and his insanely obnoxious array of death projectiles
Sonic's side-b
Zelda's side-b
Ike's side b (to a lesser extent now than in 2.1)
etc.
The game is still fun and competitive, I just wish that the developers shifted more towards giving characters better overall moves and options, instead of giving characters one or two incredibly useful moves or tactics and basically saying "Hey, here's the amazing move, ABUSE IT". Give the characters good moves, the rest will come in time. The characters right now (most of the new ones) just feel infuriating and silly. I cannot stand, for instance, Lucario, as he takes (sorry for the people I will offend) little to no effort to combo with. My friend likes to spam buttons, and now that he plays Lucario in P:M, he thinks that it is a good strategy to mash A and the c-stick. And you know what I find most saddening? HE'S RIGHT. Not that I lose to him, he sucks, but a player with more spacing and mindgames could easily open me up and hit me with a "faceroll" combo. And my friend will constantly say after getting an easy 50% on me after I eat one dash attack, "That was a good combo right?" and I have to resist the urge to go into the files for P:M and somehow remove Lucario from the game.
And I get this feeling with plenty of characters.
All in all, the game isn't unbalanced, at least, I don't think so, but it's just so gimmicky. Move away from gimmicks, please, make the characters inherently better, don't give them ridiculously stupid gimmicks to power them up.
I'll probably get a lot of hate for this, who cares. I was just playing a long P:M session with my friends recently and was getting very annoyed (not that I was losing) and I started to realize why.
. 
Too funny..... Yeah, Drinking makes a good point, but Leaf actually makes a good point too. Since Fox's usmash is only frame 7, he can WD usmash OoS just as fast or faster than any other character can WD grab OoS (which is usually a major punishment of unsafe attacks on one's shield). The funny thing is that Fox can also WD grab OoS just as fast as everyone else, but why would you grab when you can usmash? 
