I am late to the party too, but...
This game feels like it belongs with 90's classics like doom, Wolfenstein, rise of the triad, and any other classic fps you might have played repeatedly on shareware from friends on a pc.
The game itself is very straight forward. Go in, clear a room, find the treasure and continue. What makes this game unique is that you level up you gun with accuracy and you have unlimited ammo. It adds to a fun factor kind of like playing contra on nes way back when.
Played it on a 5c with out crash or issue... Totally worth it, lots of fun!!!