[lorq13]

As long as you can change ANYTHING, meaning number of planet types, number of atmospheres, speeds of seekers/boarding parties, adding more resource types, players will come up with very interesting mods. Just give them as many options and tools as possible.

I do like a great level of detail and underlying rules that players can learn and understand.

About ship sizes; if you can build any size ships, keep in mind that there should still be classes of ships for players to make all those hansom models.

Decent AI is also a must. I prefer to play against people, but learning the game still needs a good AI.