First of all, I would like to point out that I love Dirty Bomb, and I think it’s flawless, and the GUI is perfect in every way shape or form so please don’t comment about me hating.
Secondly, I think that there should be more options to edit the way the game looks for you. Biggest example of all are the reticles. The dot and the pretty ugly crosshair ones aren’t bad it’s just that they’re a bit boring imo. I know you can customize the colour from black to rainbowy with slightly crimson patterned fuscia & torquise mix with green, but I think they lack the enthusiasm and the detail. I think instead of downloading the overlay mumble reticle or any other mods, we should have either more reticle options or a “build it yourself” option where you can select the lines, how many, the lengths, the sizes, the colours, the dots, positions etc. (there is a game that does this and it’s not complicated at all).
Another thing that I think we should be able to change is where the clock is. There are people I watch on YouTube with their clocks in the top left corner and ones with the clock in the middle at the bottom (how do they get it there?) but I think it would be better if we could hold ctrl or something to get the mouse out and be able to move the timer around the screen to where we like it. The main reason for this is that I would much rather have it near my reticle rather than top left in some unknown dimension so I can see the respawn timer easier. Of course adding the transparecy of thing would also be quite nice.
Those are the 2 things that bug me quite a lot right now but apart from that I don’t have anything else I’d like to change personally. Would love to see suggestions down below though 

to scale the crosshair to a size of your liking.