Does space age change anything?

[Neolocal]

...Or does it just introduce you to the a different biome with some biome centric buildings but it's the same gameplay with the same progression of buildings? You just essentially start over to get to the next biome?

[Loewchen]

Each new planet changes progression in unique ways, things that might take lots of effort on Nauvis are straightforward on others and vice versa. If you don't mind spoilers you can check out the planets here: https://wiki.factorio.com/Space_Age#Space_Age.

[Tertius]

The general gameplay and concepts are the same, however there are new kind of challenges to master. Vanilla Factorio has rather simple and straightforward challenges. You work yourself through the technology tree, that's all. The most complex thing to understand is probably how to balance oil production with advanced oil processing. In Space Age, every planet has its unique somewhat similar challenge in spirit.

Designing a space platform to travel from planet to planet is its own challenge. It's not just for personal transport, its's essential for exchanging items from planet to planet, because there are planet specific resources that need to be imported to other planets.

And you're not supposed to "start over" on a new planet. You can do that in an emergency case, but don't hesitate to bring items from your previous planet to your new one along with you, so you have a head start. You use a space platform to fly from your first planet to the new one, but nothing prevents you from sending that platform back to your starting planet, load it with items you forgot, then send the platform to where you are currently and drop these items on your head. Receiving items this way don't require you to have a full blown working factory on the receiving side.
You also don't need physical presence of your character on a space platform or on a planet to make it perform something. Space platforms work the same no matter if you're present or not, and on a planet you just need roboport coverage where you want to perform remote control. The logistic robots work similar to your "hands" remotely.

[KillingTimeItself]

each planet has a separate "meta" that you're supposed to follow, each one presents unique solutions to the same problems. It's quite fun, especially paired with spaceships either to shuttle materials around to different planets, it opens up 5 dimensions of play, rather than the one that previously existed.

And with every planet you get access to new buildings and items that make gameplay more interesting/easier or varied. It's a really well designed DLC. Nauvis is basically the same, apart from the whole space aspect of it, but the other planets make up for that more than enough.

[h.q.droid]

The biggest change of space age is the non-linearity. The planets, the quality system, the space platform system, and the old yellow / purple sciences can be progressed independently. That creates a lot of varieties in strategy and needs to refactor during progression.