For me it would go like this (dont hate for not posting any of the very popular ones)
1] Fekete Keres - black search - awesome one! The atmosphere made me quit at one place, which didn't happen before... awesome mapping, good story and no flying guys.
2] The Mansion 1408 - veeery goood mapping (perfect!), story was also very good! What I didn't like was that it's very short.
3] The Castle Of Eberfield - it's a nice custom story with very nice puzzles and good storyline. Mapping was just fine, but there were no custom added objects. It's also long so it's a good one ^-^
4] Digressiophobia - LOVED for the idea! The idea to play with two characters at once is just OMGWTF! It has nice mapping, not many monster encounters, but just enough to keep you horrified and it's overall very good!
Well, I did play the dark room but I wouldn't put it in the list because all the ones I wrote are serious ones. Cheers