The microtransactions are obscene even for a cheap mobile game. Plenty of typos and language errors, making certain things unclear in regards to abilities and the likes. You can pay money to make the game faster, and to buy gems to allow you to 'skip' waves. The game is designed to waste your time. It seems to be meant to be active il the background, but it isn't. It's a fun little baseline, but after just a couple of hours there's nothing left but a time-wasting grind.