Every issue is paragraphed so feel free to read one or two or all depending on how much you hate/love the game.
The first and most biggest issue of this game (on behalf of PC users) has been since the DLC came out. Since DLC has been released (just by looking at the number of available games going from ~15 to 5 for TDM) it has sucked big time, at least for us here in Australia. I did not download the DLC for mw2 as I disliked the maps and because of it become increasingly difficult just to find a game I refuse to sink more money into this pitfall of nothingness they call one of the best selling games.
Secondly, this: http://www.youtube.com/watch?v=dK9Ct3vKEXc
At first I thought my mouse was screwing up. I have never tilted on online poker or COD to the extent where I would bash my mouse (Logitech G700). I spent about 30 mins troubleshooting the error and Google-ing possible errors with my drivers and/or mouse and discovered that link above and realised that it is the games fault. I consulted a representative through Activision and besides the rep being very helpful and cooperative he was unable to provide a solution to the error. This issue is still ongoing but I have tweaked some settings to something stupid by trial and error and it is at a somewhat minimum.
Thirdly, ever since DLC got released, about 20% of the servers I try to join (over a large sample) will attempt to load a map, then it will disconnect and say this error message: main/iw_06.iwd is different from the servers. I googled the problem only to find about 15 different gaming problems with OP's posts starting with: " **** this game I keep getting this message: main/iw_06.iwd is different from the servers. " There is no solution to this either (maybe purchasing the DLC will help but a lot of my steam friends say it is harder to find a game after buying DLC). I tried verifying the game cache, re-installing steam and doing all that sh*t but this doesn't fix it.
Lastly, I discovered in February (3 months after game released) the old LMG-thru-walls+aimbot hack which became very popular in MW2 about 6 months into it. They have done nothing to control this as every 1 in 2 sessions I encounter someone who will sit there with an LMG and the most recent instance was within 5 seconds of starting a match on dome where I was shot through the blue tarp.
I think it's time people starting spamming this ***** company to get dedicated servers or spread the reviews that it is a piece of crap. I never got this with mw2 even though the odd server had ridiculous ping or a bad host, but it was never this bad.
Cliffnotes: Will accept 1v1 QS with MSR for online rollz