Neutrino

This is beyond impressive. Long, feature-rich action RPG running on GZDoom, with fantastic looking maps and remarkable level of polish.

Typical extreme modern difficulty, but I'm not sure if there is a sense in complaining about that anymore. This trend isn't going anywhere, if anything it's getting more and more popular. I guess it can be appreciated for gorgeous and creative visuals even if one doesn't enjoy the way it actually plays.