The single player is a short disjointed action romp with some set pieces akin to that of a Michael Bay movie.
The Co-op play is the strongest aspect of the game providing a selection of missions which are undertaken by yourself and a friend, these vary from disarming bombs in the Favellas of Rio to one player covering the other from the gunner seat of an AC-130.
The multiplayer component to MW2 is a disgrace when compared to the experience provided by CoD4 and even CoD:WaW. Infinity War opted to drop dedicated servers for the PC making broad sweeping claims in regards to cheating being rife on dedicated servers to a majority of PC players struggling to utilise server browsers. As such Infinity War rolled out their system dubbed IW.Net which is a Peer-to-Peer matchmaking system.
The P2P matchmaking system which was rolled out by IW was rationalised as a quicker and easier way of providing multiplayer for the community which would eradicate cheaters and give players a highly accessible and quick multiplayer experience. What IW neglected to mention was that their P2P system requires users to set-up port forwarding schemes.
This system results in reduced performance as the host machine has to perform all the calculations a dedicated server would in addition to performing the calculations of the player. IW have also removed the numerical ping display, replacing it with a 4 bar system which does not provide any accurate indication of pings. Both these issues add to the poor online performance often resulting in very laggy servers. The P2P system also means that when a host quits the server has to migrate to the next best machine causing a break in the gameplay. This break can either been a short 30 second break while it transfers data or alternatively it can result in the game you were playing disappearing due to migration issues.
Another effect of the lack of dedicated servers means that hackers which are around enjoy their games unimpeded as there are no admins to kick/ban the cheats and there is no system to vote kick a player from a server for cheating.
The other major factor in regards to the IW.Net system is that it means there is no mod support and no custom map support. IW.Net allows IW and Activision full control of all content on the PC meaning that if you want more maps odds are you will have to pay for them in the form of DLC packs.
The Multiplayer Balance of the game is also quite poor with several weapons being obscenely powerful relegating many of the other weapons useless once you have unlocked these better weapons. Two examples of this imbalance would be the ACR which is an assault rifle which is fully automatic with laser accuracy and zero recoil. The second example would be akimbo 1887 shotguns (the shotgun used by the terminator in T2) these shotguns are garunteed one hit kill at ranges outdoing all other shotguns and at smg effective range.
The final issue with MW2 is that the PC was given a straight up console port. The FoV is limited to what you would receive on the PS3 or 360 and the graphics options are highly limited.
TL;DR - If you are looking for an FPS fix there are better games, albeit older games, on the market. I'd suggest consumers wait untul for the pelthora of releases due early next year.