I don't doubt it will be an awesome, awesome game...however, Melee set such a high standard for the series, and I wonder if it will meet that standard...? So what are your concerns? Anything you're worried will go missing in Brawl that was in Melee?
Here are my hopes for the game:
1) They will include the "advanced techniques"...that is, wavedashing and SHFFL'ing and L-cancelling and such and such. Yes...wavedashing was a glitch, but a glitch that they decided to keep in. Certainly, Sakurai and the rest of the developers (who have played extraordinary amounts of Melee) can't be oblivious to the competitive scene and the popularity of said advanced techniques ... hopefully...
2) Online play. This is the big one. If Brawl is online, it will be huge. It's a dream-come-true for many. I'm sure that if there was one thing we all wanted in Melee, it was for a way to play more human players, besides the same friends we played with constantly, over and over again. Online play will solve this, and will enlarge the competitive scene greatly.