I have had this on another storefront for a while, and I am so happy to see HROT come to GOG. A lot of games have claimed the title "retro shooter," but HROT really delivers. The gameplay is solid, the world aesthetic is cool, and it rewards exploration with secrets much like DOOM, Quake, and other classics. For me it stands alongside DUSK as modern games which truly understand the genre and the era.
I've been burned with other early access projects, but HROT has continutally delivered, and been responsive to input. With the second act done I can't wait for the final game, but I'm sure third act development will be fun and exciting, too.
If you love classic FPS you owe yourself this experience.