A lot of MMO's these days struggle to even capture your imagination, let alone challenge it. To expand your imagination as in allowing you to be creative is something that would enhance immersion. Will be interesting to see what can be added in the way of world shaping features, outside of the usual crafting and housing type stuff. Plenty of varied activities to keep you busy always helps, but staying within lore boundaries. Nothing kills an MMO faster for me than thinks that seem out of place, steam power race cars anyone :)