Quests can be difficult to see, with a 3D view.  Here, I’m experimenting with setting up quests using variants of buildings and roads.  In the foreground, you can see the quest giver.  The big black bridges would eventually be arrows, and point the way to the quest destination.  In this case, we’re looking at the NPC’s first quest, which involves going to an area and fighting some monsters (that area which is glowing in this screenshot), and then travelling to another location, further in the background.  The player can move these destinations around, or place more of them, or insert new ones in the middle of the sequence exactly as he places regular roads.

It’s actually a pretty nice system, I think.  It needs a lot of graphical polish, but in terms of a GUI, I think that it basically works.  Just need to make it look a bit nicer, and fill out the toolbar on the left so that you can set which quest you want to edit…