This game is a lot of fun. The content doesn't get old, the map design/layout is really great, the gameplay is epic, the sound design is not bad at all. And yes. This is from someone who has not bought beta 6 yet.
I think what needs to be improved in beta 7 however is the graphics. Here is what I would do:
Assuming you are going for a more realistic game (if you want a low poly look and feel just use solid colors and vertex colors and maybe some hand painted textures), the texture mapping should be improved. The textures of this game are not bad, but they are inconsistent and sort of out of place in the way they are used. The textures are all relatively high res textures, but the only texture type that you are using is a diffuse map (texture that affects the color of an object.) Basically, you can use photoshop or gimp to generate a normal map (texture that changes the way light bounces off a face) and a displacement/height map (distorts the texture to add a perspective effect). obviously there are pretty good tutorials on how to do this and it shouldn't be so hard to implement. You could add surface imperfections (basically just the textures I have listed above but subtle) to perfectly smooth areas on things like vehicles and weapons. it is subtle, but extremely effective.
This next thing may be a little frustrating to set up for the first time (as it was for me), but you should be able to have it down in like a day or two. That is post processing. I don't think I have enough room to post an entire tutorial on how to use post processing, but there are, once again, a lot of great tutorials on it. Basically post processing adds quick effects to each frame after rendering them. Here are some effects I always use that really make a huge difference. You might already know some of these but in case you don't:
Bloom: you have probably heard of this, basically a glow effect for any super bright pixels. It looks absolutely beautiful on things like explosions, lasers, or anything else emissive, and adds an extra kick to any surface lit excessively by a directional light.
Ambient occlusion: When you have only an ambient light, darker surfaces tend to look flat, which makes the lighting look like it isn't doing its job. Basically, ambient occlusion darkens faces based on how close to another lit face they are, making more realistic looking shadows.
Color grading: Specifically ACES tonemapping. ACES has been the standard color management system for a while any form of computer graphics looking to be realistic and/or cinematic. I have no clue what exactly this does other than tweaking the colors a bit, but it makes a huge difference.
Motion blur: I'm sure you know what this is already. All I will say is it will make the game look a lot smoother.
Things like a vignette and noise will improve it as well, as long as you don't make them too excessive.
And finally, some small tweaks you can make:
Going back to post processing, you can add chromatic aberration to the scopes. Chromatic aberration just splits the r, g, and b channels towards the edge of the screen, which would look really great for a light refraction effect.
For any rounded objects you can use phong shading, which is basically just smooth shading.
I really love your game and I think I should stop procrastinating on buying it on Steam ;)