I've not spent too much time with the NEXT update, but the major changes I can see are a balance check and rebranding of all the basic crafting items, fleet operations, and more base building flexibility.
There are also changes to terrain generation, and general engine optimizations. Gone are the floating mineral deposits and extreme pop-in. Flora and mineral distribution feels a lot more natural.
The changes to crafting take a bit of getting used to, but mostly boils down to unfamiliarity with the changed recipes. The basic ingredients can also be condensed or diffused in quality.
Fleet operations are very similar to the fleets in Start Trek Online. You can now purchase frigate class ships, which you can send out on lengthy duration missions. Missions will have an overall theme such as combat or exploration, and the different types of frigate you can purchase will have qualities that are more or less useful for particular mission types. Once the particular mission is decided, you can choose which frigates to send on the mission, and then through the duration of the mission you will get updates on progress. It is possible a frigate will be damaged, and you get a choice to recall it or remain on task to risk more extreme damage or destruction. Damaged frigates need resources to repair, and you actually need to board the frigate to accomplish the repairs.
Frigates I've seen vary in cost from around 1 million for a C class, to 12 million for an S class. Mission rewards seem varied enough to cover most currencies, items and blueprints available through other means.
I haven't dabbled too much into the base building, but you are no longer shackled to particular plots, and can set up in much more appealing areas than in earlier versions of the game. Once a base beacon is placed, then all the familiar base items can be placed within its vicinity. You can even set up your base right next to an NPC structure. I'm pretty sure the available base space on freighters is way bigger now.
There isn't any major changes to the way the game actually plays other than multiplayer now being synchronous. You will still be doing the same tasks as previous iterations of the game.