I love this DLC so much and wish more of this content was in the works.
It adds colonizable planetoids, upgrading your colony to an interplanetoidal empire. The logistical challenges this introduces are immensely fun. On top of that, many of the game's components previously unviable are not probably worthwhile to engage with on any generated map, as you're guaranteed to have roughly all biomes spread across all the planetoids on your map.
Rocketry now requires building interiors, which allows for an immense amount of customization on the fleet that you'll be building. It is also fairly forgiving to get into - for good reason, as you must first leave your planetoid much earlier than in the base game in order to progress. Many new automation options are introduced to get even more indepth into efficiency.
Radiation is introduced as a game mechanic. Not only does this introduce more depth to plants and farming via mutations, we also get a new way of killing germs & handle uranium as a resource. With the game's thermodynamics system I've always wanted to make a nuclear reactor. Now you can! Harnessed radiation travels in radbolts which comes with its own new logistics minigame.
Lastly, we get some minor quirks that are a strict net positive to the game like new critters, plants and recipes. You'll never have to engage with these if you wish not to.
If you enjoyed the main game and wish for more depth across the board, I urge you to purchase this expansion and show Klei your support. If you are afraid of handling multiple colonies, consider this: As you embrace the learning process that is overcoming ONI's countless challenges, you'll find everything rather forgiving and that there's no rush to keep everyone busy. Focus at one thing at once and in time, with mastery, you'll find your imagination to give you ideas of what to put everywhere and how to convert each resource and energy into something else. No sweat, no rush.
10/10