My favourite is definately 6085 (and I am happy to say this considering I own all the castles between 1984 and 1995). I think the colour balance is awesome, and the old fold out castle walls just work so well to create an awesome looking structure. 6074 would follow a close second.
I may just have to try building 6085 in reverse colours as suggested above, the idea intrigues me.
The early raised base castles were good (although 6081 had far too few pieces for my liking), but they lacked the value of the old opening out castles. The modularity of castles of the era simply completed the picture.
It is with great enjoyment that I will setup a 5x5 grid of 32x32's, setup 6080 on one side and 6085 on the other and let the factions wage war. (both castles increased in size with the pieces cannibalised form all my other castles).
I am still waiting to get 375 - but am finding mainly incomplete sets coming up, and would rather not pay international prices for it.
I also find that the smaller sets like 6074, 6075 (wolfpack) and 6077 are greatly enjoyable for their play value, and fit nicely into the sides of the large battlefields. - Just need more trees and baseplates
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6090 was in my opinion the biggest disappointment ever. I had wanted this set ever since I was a child, but upon building it found that it lacked the grandeur of some of the earlier castles. I think the lack of symmetry doesn't help, and it simply doesn't feel as complete as the other castles. It has a low back wall and the tower at the back right is lacking walls to protect the king.
