Epic single-player with enough variety to keep you going.
Call of Duty 6: Modern Warfare 2 might have a very long name but it's single-player campaign is surprisingly short. You can finish it in a good afternoon if you pick a difficulty level appropriate for yourself.
Despite it's length, I would still recommend a play through for all those interested in an epic FPS.
It's story elements are very well done. There are a few annoying moments where the player character dies (I think around twice or thrice in this game) but apart from that the story is an unforgettable one.
There's enough variety to keep you interested:
There's the classic war scene, where bullets and artillery shells are flying everywhere. The chaos of war is done very well and yet it never feels like too much.
Then there's the stealth sections, which are a break from the usual shoot-em-up style of gameplay.
Finally there are the odd special ops missions, which are a mix between stealth (generally in the beginning) and all out fire-fights (generally after you're cover is blown).
Nice new mechanics like the ice climbing, breaching...I won't go on. These mechanics not only add a bit of spice to the general flow of the game but also give you a sense of epic-ness and achievement once completed.
Finally, the cut scenes between each mission and the voice acting are, I think, the best I've ever seen or heard. The rousing speeches make you feel ready for anything and the characters are all unique and lifelike with realistic speech and professionalism.
All in all, a game I would highly recommend. Might not be worth the current price to some, but a GG indeed.