It's a good game but "most innovative shooter" as they proclaim is cocky indeed.
I do hope there are going to be free dlcs that make the 20 $ worthwile.
I thought this when I bought it. I already beat the story mode (what little there was) and started the time trials and the endless wave maps. I had thought that at least the game would unlock the levels on a different system than the one they're using currently (I would have preferred it to be "kill 50 enemies in an endless wave to unlock such-and-such map" instead of "kill a total of 50 enemies while dying 70 times to unlock this map"). It further trivializes the gameplay even though I like the puzzle aspect.
Another thing: the replay videos and their "Killstagram" website. Mobile developers releasing free and $0.99 games have made video replay integration almost trouble-free, but the devs' current implementation (the site) doesn't allow items to be filtered, sorted, or sometimes not even signing out!
In short, the game IS fun, but there's a lot of caveats when getting $20.00 USD worth of fun and quality.