A short single player and a crippled multiplayer for the price of sixty dollars is a slap in the face.
To top it off the networking is done with a peer to peer system which chooses one of the player to be the host. Once again a major down grade from previous PC installments of Call of Duty and other PC games which used dedicated servers to host their games. This peer to peer system which works decently for console could not suck more for PCs. since not all PC hard ware is exactly the same like the consoles this results in making the peer to peer system for the PC very laggy and unstable, unless you are the host in which case good luck trying to be the host for the rest of the games you play. Any network developer worth his or her weight in salt would have figured this out (which they did the last CoD game) and would not even consider implementing peer to peer networking for the PC. This in turn raises the concern that this was intentional and therefor a huge slap to the face of the PC community.
One more huge inconvenience with the combination of a PC game and the lack of a dedicated server is that people can make or purchase made hacks to modify their game and give themselves a huge advantage over everyone else playing. With a dedicated server any human can notice that something is awry when one person has fifteen times the kills as the next highest player, always die instantly whenever they encounter them, or even see their death wit the kill cam and notice "Wow! that was an impossible kill" and say that more than twice in the same game. They can be reported to an admin of the server and the hacker is banned. Since IW is not using dedicated servers they have to use algorithms to monitor for hackers and ban them accordingly. The only problem with that is unlike humans, their network doesn't learn by itself or notice inconsistencies that it was not programmed to noticed that a ten year old could see. The network probably barely gets updated once a month and even then if a hacker is caught the hack can be modified and improved to elude the network.
In the end Modern Warfare 2's only spectacle is its multiplayer. The single player is cool for a few hours and the special ops are fun for a bit. But people want this game for the multiplayer and since it is horrible crippled on the PC this game is absolutely not worth your time or your hard earned money.
If you would like to buy it on the Xbox or Playstation it is probably a great purchase.