IMHO, Counterstrike is one of those games that is best served with the PC.
The aiming is much less precise with an Xbox contoller. But since everyone is in the same boat, one can generally live a little longer than playing online with some of the keyboard/mouse Gods. Also, there is little/no cheating with the Xbox LIve scheme. The PC version has tooooo many cheaters.
For the $20 you're paying though, you should not get the feeling of being burned. The XBOX version has new maps, btw.