Back in the 90's they were really good. It was just more Doom 2 and it was really fun to play them. Some of the maps had some interesting concepts for the time, too, even though a lot of it was unrefined. None of the Master Levels aged very well, but still, I have good memories from them. I especially liked Dr Sleep's maps because - well, I can't quite put my finger on why, but they had a unique atmosphere to them that I enjoyed. Paradox probably also holds up pretty well gameplaywise today.