Brawl has none. Melee had the perfect amount, in that it was easily approachable, yet quite difficult nonetheless to get really good. Not as difficult as in a true, pure fighter, but more than enough that only a few very rare people made it to the upper tiers. Even there, there were moves that people couldn't do consistently, every single time, so there was still room for improvement, if not much. Melee to this day has top players who dominate. The Kens, PC Chris', etc, rarely lose, even to their own ilk. There are no such people for Brawl.

Back to the beginning though, yeah; Brawl has no depth. I've hardly played the game at all, yet when I sit down to play against players that have played it constantly since release, I only lose a few more games than I win. Brawl is a crapshoot, a game of rock-paper-scissors. There are no advanced techniques or strategies to try to pull off, there aren't really even any combos. Everything they can dumb down, they have. Even things that weren't advanced at all, but just took a little skill. For example, sweet-spotting the ledge. In Melee, you had to time it just right with your up-b so you'd just baaaaarely grab the ledge. Any higher and the waiting smash would catch your fingertips and you'd die a horrible death. In Brawl? Auto-sweet-spot. Get anywhere near the ledge, and you're golden.

Everywhere you look, Brawl is like that. It's slower, you can't do moves as rapidly as before (so that you can't combo), tripping was added to remove dash dancing, wave dashing and all the other neat moves were fixed, and the list just goes on and on.

In summary, I don't like Brawl because you can't get good at it. There are no players out there who could consistently beat most other players. I want to play Smash as a fighter, instead of just a party game, and you just can't do that anymore.