Nice little FPS. There isn't much to it, you go through levels and kill stuff. The game has its flaws and feels (or actually, most likely is) unfinished, but i think the developer had their heart at the right place.
The levels look a bit convoluted in the Hexen tradition (that the game seems to be inspired from) but in fact they are kinda linear in that there aren't any alternative paths or stuff you can do in different order (ok, there are two cases where you have to activate two switches but that is all i noticed). Also there is only a single very obvious puzzle (you have to avoid some candles on a path). You do have to find switches and there are a bunch of secrets all over the place though all you get from the secrets is more ammo.
In a way it looks like a "what if Serious Sam tried to become Hexen". While the levels aren't as straightforward as in Serious Sam (or even Painkiller) and you have to backtrack in a few areas or find how to move forward (especially with the third level which is by far the biggest one and is made up as a hub), at its core is a series of arenas with enemies spawning in (though in some cases they are already prespawned - this is also used as an incentive for you to explore the levels) and all enemies have very SS-esque behavior in that they just move towards you (and you move backwards while shooting them). Some enemies have ranged attacks and a few can teleport (which is clearly telegraphed so it doesn't become annoying) but for the most part in each arena you'll see a dozen of enemies just running towards you with no concern for their safety or trying to flank you.
The weapons feel good for the most part and they all have some sort of fantasy design, even if most of them end up functioning as the classic FPS weapon archetypes (which is a good thing in my book). My favorite is one which (IIRC is some gloves) that allow you to punch from a distance. The melee weapons feel good too - one being your fists and the other being a sword that can freeze enemies which can break after a few additional hits. However with the game having dozens and dozens of enemies running up to you and most of them using melee attacks faster than you, you only get to use melee weapons against weaker and/or slower enemies.
There is also a "blood mode" which causes everything to slow down and during that mode all your attacks also fill your health - and melee weapons become easier to use. However since it is *attacks* instead of kills that fill your health, it is better to use faster weapon unless you want to preserve ammo. Blood mode is neat and you can activate it wherever you want as long as you have enough "blood" (or whatever that is). There are two bars that fill as you kill enemies, once the first bar is filled then the second bar starts to get filled too (you can also think of them as a single bar split in two parts). You can enable blood mode while you have enough blood in the second bar - the blood depletes while you have the mode enabled and you can deplete both bars. However you can only enable it if there is blood in the second bar, but you can disable it at any time.
Sadly it looks unfinished - every few levels there is some text with story bits (though the story doesn't matter much, at the end you just kill stuff) and after the last available level you get some text that seems to imply there will be more but there isn't a "continue" button. So i guess the dev planned more levels but never happened.
As i wrote above, the third level is by far the biggest one and feels a bit different than the others who are a bit more straightforward. I think if the game was designed with a few big levels like the third one and was a bit less linear (e.g. the third level is basically a hub and you can move between the hubs as you want however there isn't a reason to do that except perhaps for secrets - but the secrets aren't really that enticing) it'd be -and perhaps be received- much better (e.g., had to complete some objective in each hub at any order you wanted so you can progress and/or unlock some other hub or area in the level).
There are also some bugs. For example the action mapping screen is finicky and for some reason it seems the available resolutions are hardcoded with the maximum being 1080p. After each level you get a scoreboard like in classic FPS games counting the number of enemies, items secrets and the time you took to finish the level but it doesn't take into account enemy spawning or items the enemies drop so you often end up with more enemies/items than the level had, making it kinda pointless (since you don't know if you missed anything). The time is also buggy as it only counts time since the last level load, meaning that if you die and reload you'd get a smaller time than it actually took you to beat the level. The secrets are *probably* counted correctly though but i don't know for sure as i never managed to find all of them.
But all in all, it is a fun short game despite the flaws, though i wouldn't recommend it outside a sale as it may either not be to your taste or not keep you entertained long enough due to the small number of levels it has.