Earth and Titan feel ok, but Nessus and Io feel unfinished by comparison. Io especially feels barren. Enemy placements seem random. In D1 most enemies were near a structure (shelter, cave, building) that made military sense. Some places on Nessus and almost all of Io enemies are just standing around random places. Outside of a major update I think by adding a fair number of roving bands of enemy patrols could make these areas make more alive. I hope this helps. :) have a good day.