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What I like about the Inferno castle is that it has a great style. I also liked that in Haven and the Barbarian Tribes, the buildings look harmonious next to the background, even blending with it. In Necropolis, I think the buildings are too "stuck on." And I already talked about Haven.
What I don't like about all the cities is that the building for hiring champions is almost always smaller and less impressive than the other creatures' buildings. Also, there are few differences between the upgraded and unupgraded buildings. The Capitols don't reach for the sky :(.
In general, the forts are the same. Although I don't think they need city screens. A 3D window would look good with the 2D city windows, emphasizing the differences between the statuses of these two objects.
I voted for Haven. I like the thoughtfulness of this castle. The gates are beautifully drawn :). I would put the Inferno and Barbarian Tribes castles in second place. And Necropolis in third. They really tried to ruin Haven, though. Although all the screens in the game look good, including the human one.