This is a nicely designed game, but it is definitely set up to frustrate you into in-app purchases. The rate at which you advance through the game is intolerable if you dont. I really hate this whole model of in-app purchases for games. It seems like it leads the designers to sacrifice game quality and enjoyment for the sake of squeezing more money out of you. Just sell the games for a fair price and code it for the enjoyment of the player. This particular game is so bad at trying to frustrate you into buying upgrades, I had to rate it as a 1 star app, especially when I contrast it with their PC version. The PC version has a single flat price, has no in-app purchases, and doesnt frustrate you into upgrades just so you can complete the missions in a reasonable amount of time.
Mozarts Disowned Son about Defenders: Tower Defense Origins