While it's certainly an original concept for a game, I find it overly mathematical for my tastes. This is not your average roguelike; you must think well in advance of what items you will be using and count precisely how many steps you will take and think of what items you'll switch to mid-fight... all well in advance.
There's a fine line between fun and mathematics. Unfortunately, this game lies on the wrong side of the divide.
That aside, the NotEye engine that comes with it can be used for several games and provides an impressive range of capabilities to graphically enchance our much-beloved roguelike games, from Angband to NetHack to Brogue. Make no mistake though; Hydra Slayer is a full-featured, no-nonsense game. Its famous engine though is what really steals the show here.