Short single player and disappointing multiplayer.
Dedicated servers allow for communities to spring up, and provide a sort of home where gamers know they will find the experience they want with friends they enjoy playing with. Mods extend the life of games and customize the user experience, their exclusion is an obvious attempt to bolster DLC sales. Infinity Ward touts changes to the multiplayer experience as an improvement and streamlining of a dysfunctional system. They are wrong. Host advantage, small server capacities, and high latency are not improvements. The loss of communities and competitive play are definitely not improvements.
MW2 on the PC is a rent or borrow; anything but a buy.