Did you know it takes 20 biter eggs to spoil into 1 big biter? By default, with Eggs, it is 1 to 1. The hatched tier is dynamically chosen using the current evolution.
Mods introducing new content into the game.
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.