I've been playing extensively over the past couple days. My thoughts:
1) within the first five games I joined, i found two obvious hackers who were making sprints megaspeed and gravity ridiculous. A couple hours later I found another hacker who was spamming the AC130 big rounds. I left very quickly. Couple hours later I killed a guy, and instantly got to level 70. Cool. Then he started spamming the AC130 too so I left that game.
2) the team matchmaking is absolutely horrible. I hate how bad the teams can be in this game; I've never raged so much before while playing counterstrike, and I rage a lot when i play CS.
3) witchblade is ridiculous. its so powerful. i spent about two hours getting the usp kills for it, and now i can run around murdering everyone, until I get to...
4) the lag. IT SUCKS. I can't tell you how many times I thought I've stabbed someone or rounded a corner or put a bullet in someone's head and not have it register. I've always thought this, and now I've seen it in action - Infinity Ward's decision not to have dedicated servers was the most FUCKING STUPID decision they could ever have made. I don't know why they thought it would be a good idea but obviously when I shoot someone in the head three times from point blank range, then die to a knifer without having any of those shots register, something is wrong. which leads me to my next point...
5) headshot detection is pretty much BS. I don't know how big infinity ward thinks human heads are, but in this game it definitely seems like the size of a fist. Either that or all the guns are horribly inaccurate from point blank range. If i'm standing to the side of someone with a pistol two feet away, chances are I'm going to blow their skull off in real life. Of course, in MW2, this doesn't happen, and they can take 2+ bullets to the head/neck area and still whip around, fire two shots with a barrett and then swing a knife at my face.
So, while the free weekend was fun, it's verified everything I thought was shitty about this game and probably made my mental health take a turn for the worse. In short, there's no way in hell I'd ever buy this game on a PC.