The one place I really missed diagonal movement was in the Animated Forest. Not being able to move diagonally made it much harder and a lot more tedious to get through. I don't know if there's some way of making it a bit more bearable to compensate for the lack of diagonal movement, reducing the number of trees slightly or something maybe?
That's actually an excellent point. We haven't yet looked at the implications of the changed options to older maps. To be honest the current living tree level was initially created to see how well the game performs with a ton of monster - and we basically are in the same state as we were for it in the original ADOM for a couple of versions: Performance is not yet where we want it to be and things will gradually improve.
So actually redesigning the forest level for non-diagonal movement probably is the best way to go and I have put it on our list t be addressed.