I quite like these 3D tower defence games, and I wish there were more out there. I think you've done a nice job making the whole tower defence system, with turret placements, enemy waves, etc. Generally, it's quite enjoyable. I've encountered a slight issue where some enemies got into a place where no turrets are able to hit them, causing a direct loss from that. I've managed to still stay until day 4, though.
Other things I like:
- I liked the turret models for some reason
- Interesting hill map for a tower defence game
- Satisfying particle effects and sound for the bullets
Suggestions:
- May be allowing new turret placement locations through the game? The current placement doesn't seem enough
- Turret upgrading is a staple of tower defence games. It would be nice to have them as well
- Consider adding a damage animation for the core tower. A blink of red will do the trick