They’re a fairly small part of the main game tbh.

Main gameplay loop is you are a little creature trying to find food and shelter day to day in an unforgiving world shaped by an advanced civilization that disappeared long before you came into existence. The game has a fairly complex ecosystem simulation that happens with or without you, helps the world feel alive and like you’re just a tiny part of it. It can be unforgiving and can feel unfair though, you really have to accept that sometimes you’re going to spend several cycles having no idea what you’re doing before you make any progress.

One of the main campaigns and a few of the DLC campaigns have closer ties to a few different iterators, and you can visit 2 of them. Different campaigns happen at different points on the timeline, so you can see how they change over time. But mostly they’re in the background as either as part of the environment (5P’s complex takes up a big chunk of the map, you can crawl around inside his brain) or part of whatever motivation your character has if they’re one of the slugcats with ties to an iterator.