The fact alone, that your game doesn't randomly crash* or contains the RRIS** is a really important aspect for me .
Also: It's already playable and the graphics look nice.
My only possible suggestions for improvements would be stuff like moving on the map by moving the mouse cursor to the border of the screen or keyboard shortcuts for stuff like drilling the wall (maybe close to other keys like the one for teleporting Rock Raiders down).
*I tested a base with hundreds of Rock Raiders (around 370) and I didn't even encounter low framerates. That could be partially due to my computer and the game engine, but it's still great.
**(Rock Raider Idle Syndrome, yay for made up medical terms)