Start underground. The Nauvis surface is hostile and normal surface construction is forbidden; dig out cave space, use shafts, and build your factory below.
Large total conversion mods.
Transportation of the player, be it vehicles or teleporters.
New ways to deal with enemies, be it attack or defense.
Map generation and terrain modification.
New Ores and resources as well as machines.
More than just chests.
Am I missing how to get wood or small electric poles, or is the lack part of the challenge? Distributing electricity seems a bit much.
Edit - nvm. I'm not great at noticing things and missed the stairs up to the surface, where I see trees.
Can't see the forest through the tree's! ;) It got me for a minute too!