I've had a lot of great games on ns_nothing, and it's the most fun for me to perma-gorge on it. Granted it is a large map, and the elevators hinder movement more than help, it's still very solid.
On the opposite end of the spectrum, we have ns_ayumi. I honestly don't beleive anyone enjoys this map for the gameplay; It has a few pretty hallways, like the snow between marine start and AE35 hive, and it has the "OGM CATBUS!!11oneleven!" secret room. I think the gameplay is horrible; Marines have too many easily-defendable seige locations outside of hives (A skulk spawning in AE35 has a 0% chance of survival because of that long hallway), movement around the map for an Onos is a pain because of the many small corridors, and most of the vent systems that could lead to a possible ambush location against marines are weldable. Plus, if the marines set up the node in the gorge's hideout and electrify it, they've effectivly cut off movement through that vent for any passing skulks.