Not a bad game, you do have to agree to some data collection apparently and one line has something about collecting your social security number. I just assumed that, the line was more for korean players.
It's like a horizontal tower defense game against various undead, mostly zombies in the early stages. There's a lot of rpg elements such as leveling, talents (which can be retrained at no cost between stages), gear, skills, and mercenaries (which can also be leveled up by pouring money into them).
No IAP blatantly stand out as being a must purchase so far. No time based blocks that prevent me from playing. Any strong enemy so far that I've died to have been due to me not properly utilizing my abilities and stage layout to my advantage. Additionally, I probably could grind out gold in order to level up various aspects to overcome them as well.
On a retina display the images are a little blurry. The "main" attack also sometimes does not want to stay pressed sometimes.