Subnautica is one of my top five games ever. I sometimes replay it just to relax, I love the loop of gathering resources, scanning technology, always improving... there's always something to do.
I played Below Zero twice during development. Once right when it came out, at least what little they had, and once back when they did the big story revamp update. I didn't like it anywhere near as much as the original. Now, I never played the original Subnautica until it fully released so maybe I'm about to be pleasantly surprised by the final polish, but I dunno. For such a similar game it just didn't feel like it had the same satisfying loop. Still fun but not 'one of the best games of all time' fun.
These are comments from the old story that was mostly scrapped but I'll spoiler tag them in case anyone wants to go in fully blind. Below Zero in the original story had a space station your sister was on and you regularly interacted, sending each other gear and such. A lot of people on forums complained that they lost the charm of the original Subnautica where the main character was completely alone, but I actually liked that way better than what they turned the story into. It doesn't need to be a carbon copy of the first Subnautica, having space station drops and missions was fun and different and I'm sad it was almost entirely removed
I agree with this. It even makes narrative sense, since 4546B would have become quite a hot (cold?) destination after Ryley likely spilled the beans about how rich in resources it was. Of course there would be other people there. You can still do a survival horror game without being alone. ---