The store where I got it had their sh*t together pretty well, so my wait was only about 25 minutes. I didn't even really get there early or anything.
My first impression was that I didn't like it quite as much as the original. Between the different shield system and the different jump, it feels really foreign. I feel like some aspects got a little oversimplified (no fall damage, no health, etc.), and the dual wield takes some getting used to (and then it does in fact /pwn all).
I've given it most of the day, and I like it now. I'm having a good time with the campaign (no spoilers, but I sure am glad that I got to do that thing that I wanted to do- around level 5 or so ) and the bit of multiplayer that I've played with my bro was pretty fun. It feels different though- it plays like a combination of the original Halo and Perfect Dark for the good ol' 64. The levels definitely are a change, much bigger, more open, and generally cool- it plays almost like some war games that I've played, with snipers hiding and stuff like that.
I was a little sad about the loss of the awesomeness of the pistol, but the carbine is pretty similar. I've found that the old pistol/shotgun combo is no longer the dominating weapon combo- I like the dual wielded needler/SMG combo for pretty serious ownage.
Anyway, at this point, I'm really digging it, even though it's really different from the old one.
I give it 9 thumbs out of 10, as of now.