I think the Smart Hammer™ is safe. I was able to defend it for 16 minutes until the game was overloaded with information and stopped responding. 😁
I think you could have increased the difficulty a bit more after 5-6 minutes because right now you don't even have to shoot to stay safe, just place all the towers.
The music fits the game perfectly. The graphics are simple but I like the color palette and CRT monitor effect, also it's clear what is happening on the screen.
Overall, it's a fun and enjoyable game. Great job!