The vignette effect is a matter of taste. Personally I like it, but I van understand disliking it. I agree that there should be a way to disable it.

I uploaded three pictures that should show everyone what effect the vignette has in your screen. You can toggle that on/off but you need to toggle it off every time you get in a server. It annoys me to see those lines in my screen because they're ugly. That vignette doesn't do anything else in the game other than what you see in those screens.

You need to watch the pics in full screen. If you can't see them well then you need darker background. They're more obvious when playing the game than in those screens.