Actually, they changed ALOT of things. I tried it tonight, it may as well be a whole new game as far as I'm concerned.
Aside from a giant pile of new content (they call this a SMALL update? Seriously?) there's the new survival mode. This is one of the reasons why base-building is in before multiplayer. Because it helps you not die horribly as the game gets continuously more cruel. It has a variety of practical uses that you need later in the game (such as an area to grow plants in, among other things). It's not just a pretty box to jump around in. Also, you use a portal to travel back and forth to it like in Starbound.
Survival mode is.... brutal. Utterly brutal. The core gameplay loop is no longer "pop resource, wander, pop resource", because the game is non-stop trying to murder you. Everything is deadly. Everything. Most players are having a bloody hard time even reaching their damn ship after the game starts. They get killed by weather, gravity, sentinels (even the basic ones can beat you over the head with your own face now), horrible little poodle monsters, angry plants (I hate those things... so much...), your damn shield falling off for the 103509275th time... Pirates in space are also outright murderous now, and aside from just being outright stronger, they have new AI. Old exploits no longer have any effect other than killing you. And good luck defeating a marked pirate. So the game has gotten to where a "survival" game really should be. I mean, those all have repetitive resource gathering... but they also have high difficulty and the universe trying to wreck you. Now this finally does too (and the lack of it had been my own central complaint). A lot of "quality of life" improvements too, like a quick-inventory function, and the ability to scan planets from space to see what sorts of resource nodes they actually have on them. Since everything is so freaking dangerous now, you need to be choosey about where you go. Also: the landscape isn't drowning in resources anymore. Good luck finding the things that keep life support going, among... everything else. You have to actually explore now, to find what you need. Carefully, and quickly.
This is in addition to the ability to buy giant freighters (which you can build inside with a similar interface to the one that the bases use), and a bazillion new items, and.... yeah. There's ALOT here. I wasn't expecting any of this. I was expecting a rather small update with simple little things. Not a "HEY GUESS WHAT, TIME TO RELEARN THE GAME" followed by lots of angry stabbing.
Apparently next is a "big" update. My own theory is that this next one might be the one that adds multiplayer, as the stuff that they added this time seems like a great foundation for it (and that's what the update is called, the "foundation" update).