I just finished playing Plutonia revisted, a 30-ish levels wad made by many different mappers with to aim to look, play and feel like Plutonia.
It was really good and did feel like Plutonia.
A good variety of different style of levels.
I didn't feel like it was as hard as Plutonia, but maybe it's because I've become better at Doom since then. The first levels felt like they were the most difficult (or maybe it was because I was the most drunk...)
Very enjoyable wad.