There were a couple areas where I felt the game could have been better. For example, the UI at the right side of the screen was confusing - I couldn't tell which was my currency at the start, because they're all just lines of white text. Later, I started collecting power crystals, but I didn't see any purpose for them. Maybe I needed to upgrade the towers more?
The enemies never posed a threat. I stopped adding more towers after round 3 and still made it to round 9, where the enemies just started circling the island on the right until my towers eventually picked them off.
There's also no feedback on the enemies. They don't make any sounds or react to being hit or killed. I think that's a huge area that can be improved, since the majority of gameplay is watching the towers shoot the enemies.
Overall, I think this is a solid representative of a TD game, but I can definitely see a few things you can do to make the game better!