Explore underground caverns, but beware what other creatures lurk in the dark. Bring some lights... and some guns
Mods introducing new content into the game.
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.
Map generation and terrain modification.
New Ores and resources as well as machines.
Changes to power production and distribution.
When you place down a quality belt it produces a regular belt on the other surface. I think quality only affects the health of the belt but I thought I'd mention it.
Good catch! I will fix this in a future update