Most of the reasons why I love this game Hsu already explained, It is so far beyond that of CS in many ways. First off there is a prone and run button which is awesome. Levels such as avalanche, anzio, and caen2 I can play over and over for hours and they never get old. There is no respawn wait like in CS, there are tons of dark corners to hide in and wait for people who like to camp.
The weapons are awesome and there are a large number of them to choose from. Just last night I was playing it over a LAN with some friends and I was playing as an American sniper in the beginning. Now a sniper comes with a rifle, pistol, and a knife. So as a challenge I stopped using the rifle unless i needed a long range shot, and switched to using the pistol and knife. Oh words cannot describe the sheer joy of jumping out of a 3rd story window onto the enemy and gutting him where he stands.