Absolutely outstanding! Very intense, very fun too! The multi-player is also excellent.
True the single player is a bit short, but WOW it's great!!! It's very well paced and very intense! The balance of game play is also very good. It's not so hard that it's no fun. I found that on the recruit level I could run through the whole game fairly easily. The higher levels dish out as much or challenge as I could handle.
I also liked the different tasks and functions that were available during the single player game. For example the AC-130H Spectre Gunship sequence was a great change of pace!
Another nice feature is being able to play any mission once you have completed the game.
The multi-player is also excellent. Similar to CoD2, but has additional game types. It also allows for additional skills as you advance. Lastly, I really liked the ability to create weapons profiles and select the weapons you really want.
The Single Player game is great. With the excellent multi-player game too this makes the game well worth the money!!