I was very confused the first few minutes I started playing this game, from things such as wondering why the long range tower I built didn't seem to do anything, to why I could complete the first 3 levels without building a single thing, or why enemies sometimes seemed to just vanish.
Even as I figured things out, more things kept eluding me. Many of the problems stem from a lack of feedback from the game.
Like, the AoE towers (presumably) hurt the enemies, but there was no visual indication other than the enemy suddenly disappearing after the tower made a beep. I had no clue why I couldn't play any cards after a bit, or what the blue chip with a number meant. Again, I did figure it out in the end, but I don't like that it had to take me that long to do so.
I wasn't even sure where I could place the towers at first. It took a wave to understand what was a path and what wasn't.
The idea was good, but it was the lack of visual feedback that killed it for me.
Lastly, and this is a question for tower defence games in general. Why a wave timer?