Finished the game. A cool ending. I found the late game challenging, as the locations you need to go are not easy to find, the clues you are given are cryptic at best. But the harder the conflict, the more glorious the triumph, or something like that
I really like this game, how it does not hold your hand. It more or less forces you to figure it out. I know I have to find a certain location, but no clue where it is. That not only means all points of the compass, but the whole vertical component as well. Is it north, south or down? The only way to know is to keep looking. And when you do find it, it's very satisfying. Just about every game these days has quest markers of some sort, pointing the way to the next objective. In this game, I sometimes wondered what the objective even was, not to mention where it is. But I kept at it, and went places I really would have preferred not to, in search of whatever it was. The pieces began falling in to place, things I had encountered that remained a mystery were taking a shape, it all started to fit together and it propelled me through the late stages. It's not an easy game if you avoid spoilers. But when it ended, I felt good that I had seen it through.
If I had one tip it's to use beacons extensively. Seems obvious, but it's such a time saver when you can precisely navigate. Biome transitions, cave entrances and exits, thermal vents, resources, wrecks and whatever else you want to mark. Not only to find them again, but to mark routes to other locations, or to avoid threats. The lifepod beacons are useful too, after you've located the pod, to use as signposts, just turn 'em back on as needed.
Subnautica is an interesting game. It's really the only survival game I've played. It's part exploration game, part basebuilder, part resource gathering and management. It's beautiful underwater, and so foreign and fantastic. For me it was a treat, as it's entirely different from anything I've played. I found it engaging and interesting, fun and at times frightening. It's not for everyone, I've mentioned self motivation a few times in my comments. You need to pull yourself along. I found plenty to do, as aside from pursuing the story, I also spent time building four complete bases, and at times just going for a swim to check things out. But after finishing I checked the Steam achievements and only 6% of players have finished the game. So Subnautica manages to lose a high number along the way. I would suspect that the lack of tangible progress at times plays it's part.
I found it suited me, the sense of challenge pulled me along, as I wanted to see where it went. Deeper, yes, ever down