Great game! I had a lot of fun. Very addictive. Couldn't pass the 3rd round though. Felt like a big step in difficulty.
- A tutorial would be nice to teach the basics.
- I found that the effect of upgrades are not very noticeable. Perhaps upgrades could be stronger?
- Would be nice to be able to downgrade a tile to get back an upgrade.
- Also being able to upgrade several times the same time and combining different types of upgrade could give the game a bit more depth.
Well done!