It's a good start, and looks cute but I have criticisms:
Around the time you hit wave 50, the repetition is way too boring. You're just waiting to be at the same point again, nothing interesting happens. Just grinding for crowns to get a little bit more damage and try again.
There is occasional stutter and it froze entirely once. Fortunately it saves a lot so I could just refresh. Just clicking around on the permanent upgrades screen will randomly freeze it.
Arrow rain does virtually nothing. Even if it did do something, due to the exponential nature of the enemy's power and the player's, it would just be useful right at the end to get maybe one more wave out of it. The same goes for the repair ability, except that one actually might help that one time. If I am still looking at the game by then.
I am never really a fan of economy upgrades. Not the ones inside a round and not the permanent ones. All upgrades boost your economy, economy ones just do it in the most boring way imaginable. It's also really unclear how much money to hold in reserve to maximize the money lender yield.
With the upgrade that gives me starter towers, I don't see any way to get cannon or frost towers ever again.
Is there a difference between castle health and wall health?