One of the things I loved about SE3 (besides the zoomable galaxy window
) Was the fact that you had 7 different types of worlds. This forced you to individually research the different atmosphere types and made the colonizaiton part of the game much more interresting i thought.
I think it would be great if you could separate the atmospheric processing tech into techs that would only process one type of atmosphere per tech.
Making you choose the path slowly rather than opening a full 1/3 of the planets to you in the begginging and then being able to colonize 2/3 of all the planets in the game after a single (albeit expensive) tech
All in all I think the colonization/planet setup in SEIII was superior to 4.