A simple game, your spaceship is much like a citadel and will be hoarded with enemy ships. You can obtain some in-game currency which can be doubled when you watch an advertisement, the grind is a bit on the difficult side but you can upgrade your ship. The waves sometimes are tedious, but sometimes they are easy enough to fend off. Worth your time when you are waiting for a friend or in a traffic-fast phase wave-per-wave enemies, but yeah, the grind will be too much for some people.