Honestly one of the best retro FPS I've played. It has the heart of the classics, but also its own creative ideas, interesting boss fights and a charming story. It runs well on old hardware. I just wish it went more in-depth with the YOUREALITY story and it's not really clear how you unlock the different endings. The English translation could be better and it's missing mouse sensitivity settings, but it's fun as it is.
I wanted to replay it on hard difficulty, it has some extra features (new weapons, enemies throwing grenades) but it becomes impossible after the robots appear, I couldn't beat the ninja boss.