I wanted the game to feel like a traditional tower defense game, except with you and the AI switching roles. So I didn't want to add any mechanics beyond just having to overwhelm their defenses with your units. That would have felt like cheating. I wanted it to just be the AI playing the game exactly like a human would, and the human player playing the game exactly like I imagine the AI would: building an army off screen somewhere.
The idea was that it would be a bit rock-paper-scissors-y with certain units being better or worse at dealing with certain tower types, but a lot of the mechanics I had planned got cut for time. I had intended there to be a lot more strategy.
And my AI is almost too good at placing towers. I randomized it a little bit so they don't always place them at the exact optimal positions, but I think it needs to start picking from the top 10 best spots rather than the top 5. I was so paranoid that if it chose from too wide a selection the AI might do things that look really dumb or that it might just make the game too easy.