I really enjoyed playing this entry. I did find a couple bugs, though. The first has already been mentioned, after my first play I kept the unlocked towers. The other being that once I selected a tower to place it wouldn’t let me select a different tower so I had to place the one I had chosen. I found that made it harder to react to the sudden appearance of an enemy.
I found it fun to play and I have a strong urge to master the game. However, there are a couple things that would help with strategic playing - in my opinion.
- The planet rotation is a little slow so I often don’t have time to rotate and wait for the gun tower to lock onto the enemies before they attack
- It would be convenient to have forewarning of which direction enemies are coming from, prior to them appearing on the screen.
With those two changes I reckon my avg. play time would be much longer, giving you time to introduce more challenging enemies.