One of the most brutal is "The Great War of Dracon's"...
The game took almost 30 months, it was incredibly exhausting.
I downloaded this map and took a look. The design and content are good. However, the author really overdid it with the monster strength: it's possible to play normally on an M-map in 6 months, but 30 is even longer than it took me to complete the longest map, "Jedy story." If it weren't for that, I would have played it myself.
(Василь Симоненко. Люди – прекрасні)