New places to build more factories.

Augmented or new ways of transporting materials - belts, inserters, pipes!

New ways to deal with enemies, be it attack or defense.

Changes to enemies or entirely new enemies to deal with.

Map generation and terrain modification.

New Ores and resources as well as machines.

Things related to oil and other fluids.

Related to roboports and logistic robots.

Furnaces, assembling machines, production chains.

Changes to power production and distribution.