This one is tough, but worth it. I'm sure a ton of WADs got their inspiration from the level of difficulty this one provided. Instead of big sprawling levels with a ton of low-level garbage on them (like its Final DOOM companion, TNT), Plutonia opted for tight, compact levels with interesting enemy placement and variety. A lot closer to the rhythm we got out of the modern games, wherein combat almost felt like more of a puzzle at times, but also wasn't afraid to turn it into a matter of reflex and punishment for sloppy playing. There were some absolutely bonkers levels, like... I think Twilight was the name of one? I have an extra save of it because it was insane, just no breathing room at all. And "Hunted" was great, nothing but Archviles teleported across a labyrinth. Clever and cool concepts, big fan and looking forward to others like it... as long as I actually have the skill and ability needed to play through them!