This is unironically pretty good! I don't think it's necessarily a new idea and the implementation isn't perfect but I enjoyed this. The music and sound effects are a good fit but it seems like some of them are ripped from other games. Especially what I think is the wave complete sound from CoD: Zombies.
Some feedback:
- The planning phase seems too quick. It may be better to lengthen the time and offer the player money for ending the phase early.
- Constructed walls seem very thin. It might look better if constructed objects were thicker.
- Do walls shoot primitive cubes? It would look better with custom sprites.
- It can be hard to build from an FPS view. Planning would be easier from a top-down perspective.
- The weapons list on the right of the screen makes it seem like you already have all weapons unlocked. Hiding or dimming weapons you do not have ammo for would make it more obvious.
- Some UI elements take up more screen space than they need to. Scaling some elements down may make the interface easier to look at.