I'm impressed, very nice job!
Let's start with the negatives and weird stuff:
- I went with the camera at the edge of the map and I saw 2 enemies falling in the air under the floor. It made me laugh! ^^
A camera boundaries would fix it easily though for the enemies, I'm not sure what happened.
- The AI is a very difficult field to work with, I know it well trust me! ^^ On the map with the walls around the base the AI was stuck on the left parts of the walls and I didn't have to worry about them at all.
- The upgrades system seemed kinda complex and I thought you would have to do in game, but I understand you didn't necessarily have time for that.
- Placing the turrets on slopes was quite clunky but I know it's not easy to implement.
Now for the positives:
- It has good RTS vibes! RTSs are the hardest type of game to prototype for a MVP.
- GUI style is simple and matches well the game type. (Robotics / RTS)
- The simple 3D models are looking good and the animations (Mixamo! :P ) are working well with the game.
- The upgrade system offers some replayability.
I did take time to share the negatives and weird stuff so that you can fix it because I think you are capable of making an RTS game which I said is very hard to make IMO. I think there is potential for something more serious!