A great tower defense game! I like how you have to bait the birbs into the cages which forces you to build your base around being able to bait birds and reach towers quickly. The birbs themselves are pretty dangerous if left unchecked so having the cages is just good to have even if you dont have the tower complete. The economy is pretty balanced and the escalation is paced well.
Also it is a novel interpretation of the theme which ditches the timers or sequential numbers which many (including myself) went with.