Pros: I really love the background image. I can see that you have a keen attention to detail. It's very cool. Very original as well. Not like all those same "googled pic converted" GUIs. Nice job on that.
Cons: The CS:S logo really gets in the way of the background image. And the menu is quite hard to read. That kinda cuts into the functionality of the image. What use is a menu background if you can't see where to join a server!?
Improvements: I suggest that you Change the color of the menu to something that can be read more easily. Perhaps black? Or something else dark. Also, removing the CS:S logo completely would make the GUI a lot better in my opinion.
Notes: Excellent background image, but the GUI itself just has a few flaws. Keep up the good work though!