Love the core gameplay elements!
I think the use of control to make friendly fire a problem is a nice one.
And the level design, placing the player in situations where it is difficult to shoot the correct target, is well done and executed.
But,
- The choice of colours for non-gameplay parts like GUI clash too much with the game sprites. Having the game sprites be simple is not bad, but having a good distinction between the game and menu is important, and makes the game feel more polished with little investment in time.
- Adding sound and music goes a long way, having some free generic lazer effects would have made the game feel more responsive and less sterile.
- Improving the hitboxes would feel good too, some of the bullet collisions mid-air feel really bad, especially when the sprite clips the ally pieces slightly mid projectile shot.