Okay, so I have about 23 hours played (lvl 43, but they count playtime as in lobbies as well, not just in game) on MW3 so far and the lag right now is outrageous, although I'm willing to give it the benefit of the doubt that its just because nobody's on or because their servers aren't quite all up yet or something like that.
Okay, with that said, every single gun in the game is WAAAAY too easy to use. They're all like the ACR pretty much, with no recoil, and they kill in less bullets. What's even worse is you can add perks to the gun itself. I actually like that idea somewhat, but one of them is called "kick" and it takes even more recoil off the gun. Crazy.
The killstreaks aren't actually that bad. I thought they were going to ruin the game with being way overpowered , but the only one I've seen that was crazy is the ac130. Another point streak that you can get is called something like "ballistic vests" and you can give them out to your team mates. This is actually pretty frustrating because it's like juggernaut from CoD4, but only 10 times worse because there's no stopping power to balance it out. It's basically a pain pill that you wear until you die. Stupid.
Some good points are the maps are pretty cool, although the rotation seems to favor only a few of them, I've played around 60 games and I've only played Seatown once, which is a shame because it's a great map.
Also, like some people have said, it's just crazy easy to quick scope. Hit detection seems really good in this game for all of the guns, but me and my friend were messing around in a private the other day and, yea, we were pulling off some pretty disgusting shots and we don't even snipe. So I have a feeling there is going to be a crap ton of people complaining about that.
Another negative note is the Theater mode is worse than Black Ops. You can't view other peoples gameplay unless they put it in their Vault (file share), you can't view games with a party (only by yourself), you can't view other people in the game in first person (only free roam or third person), and you can't check your score until the end of the match. Also, the controls, while they look the same, are significantly different, and feel wierd. In fact, the only plus side is if you watched a kill cam in the game, it also shows up in theater.
So yea, it's hard to judge the game right now, because like I said, it's lagging so hard I'm barely breaking even in most games, but it seems ok. Not good, great, fantastic, but just Ok.
For all those people that were wondering though, it doesn't feel like a MW2.5, it actually feels like it's own game. If anything, it feels like a CoD4.5, with a lot more killstreaks.