So I was able to log about an hour and a half last night before the servers pooped out around 8:00 Eastern.
My initial thoughts? It's pretty good. I like it... For now.
The Good:
The new feel is very refreshing. Whatever they did with the engine... It worked! Game play was very smooth for the most part.
Graphics and textures are amazing.
I'm enjoying the customization associated with the new class system.
The Bad:
The explosives are back too being very powerful. I'm not gonna say overpowered, they may be just right, but it'll take a little bit of adjustment to get used to the effectiveness of them.
The pointstreaks are very powerful as well again. Sort of MW2 esque. Again will just take some getting used to.
Same thing with the maps. I love the design and traffic flow of the maps, but they seem to have the verticality element of MW2 and BO back. Where they flattened the maps in MW3. So again, this'll just be an adjustment. I was used to not having to look up in windows and what not, now I'm being shot from above constantly.
The sound is "mushy" like all Treyarch games

The menu interface is also cumbersome and clunky like all Treyarch games. It's just another example of them doing too much, when we really just want simplicity. They did the same thing in BO, when they allowed kids to design penises to stick to their guns and smiley face reticles... Who cares about that? What does that really add to the game?
The lag compensation code still needs some tweaking (as it always does). I experienced my fits of nerd rage due to what I refer to as "insta-death". It's basically when a guy turns a corner blasting and you instantly drop dead and never had a chance to win that gunfight. That's you getting the short end of the stick on lag compensation. Don't get me wrong, I've been on the other end of it too. It's just one of those fickle deals when you've got multiple users on different connections.
I do like the guns, they all seem very strong, but they also feel very polarized like in BO1. What I mean is that the guns in MW2 and MW3 all seem to have distinct characteristics and play unique. Where as the BO guns seem to all be the same gun, re-skinned with a different sound.
While that list seems long, I'm very optomistic about the game. We'll see. I'd definitely recommend anybody on the fence to get it and try it. A few games in I was close to declaring this one "best COD ever" (espcially after going 30-8 on my first game) and a couple games later I was back to my usual fits of COD rage.