This game is great! A beautiful little love letter to the first person shooters of olde. Feels like Blood (with a big ol‘dose of Texas Chainsaw Massacre/Thief/Matrix/... thrown in), plays like Quake - and it proudly wears its inspirations on its sleeve, yet it manages to be entirely its own thing. It's derivative without *feeling* derivative. The love that the dev has for these games oozes from every pixel. Speaking of pixels: The graphics in this game are way better than the promo screenshots make them out to be. Screenshots can't really do the levels justice. Some of the level design looks downright inspired, beautiful even, with lots of nice attention to detail (for example, there is one bit where you ascend a flight of stairs to a snow-covered hilltop and the stairs become more covered in snow the further you go up). It's dripping with atmosphere and even manages to be genuinely creepy at times.
In short: This game doesn't just try to recreate oldskool shooters, it recreates the very best parts of them. It gives you that same sense of awe and those "Wow, that was cool!"- moments. It has that wonderful, unique mixture of creepiness and silliness that these old games had, where rather than being at odds, these two elements complemented each other.
My initial playthrough took me 10 hours, with another 2-4 hours of finding the secret levels and hunting for achievements. Multiplayer supports Steam/Galaxy-crossplay, however you will find most matches to be sparsely populated at best. Mod support is planned for the future, hopefully Steam Workshop integration won‘t preclude gog buyers from participating in the modding community. Until then, one thing is for sure: This is a damn good game.