This game is a fairly fast-paced game. The tutorial is quick and let's you get right into the game. The music is reminiscent of an 80s sci-fi action movie, and some of the graphics definitely put me in mind of the original DOOM. The only gripe I have is the enemies are spawned via a sort of slot machine system, which is cool because you never know which enemies you'll be facing, but it also can make a level nearly Impossibly hard, or boringly easy, but there is LOTS of in between that make this game fun and engaging, without being tedious. Overall it's a fun, enjoyable game.
On another note, this game contains NO gimmicks, like micro transactions, or an energy bar that refills over time, so you can pretty much play as much, and as long as you want without filling out more dough, which, in my opinion, is an AWESOME thing, since this is starting to frighteningly become the norm of some app games.