Just finished Subnautica. It was pretty good. Interesting water world to explore, scanning things was fun, finding new upgrades and things to craft almost always felt significant. The world was really pretty with a lot of really striking vistas and descents into dark unknowns.
There were quite a few flaws as well, though. The game was kind of buggy for one thing. It was more than once that my Seamoth became stuck underneath the terrain and I had to use the console to warp underneath and retrieve it. Things falling out of the level was just a problem in general. Several times after warping through a gate there would be big predator fish swimming around in the air. Schools of fish constantly swam through my base, and kelp clipped through my cyclops. There was a time I randomly couldn't drop an egg into the habitat and had to spawn a new egg for it to work. Also, not really a bug, but there were a couple times I accidentally dropped an important tool and had no recourse but to use the console to spawn a new one. The scanner room should really be able to scan for dropped tools, but it probably doesn't matter because they'll probably fall through the level eventually anyway.
The vehicles were just not really good enough. I remember after using the Seamoth for a while I was really wishing there would be an upgrade to make it go faster, and, as it turns out, it's the fastest vehicle in the game! It also really sucks that they lock it out of the end game by not giving it the full depth potential and heat resistance.
The Cyclops seems really cool. It's like an actual submarine that you can walk around in and you can even use the base building tool to build additional storage and furniture and plants or whatever and make it feel like home. You get 3 cameras that give you a great range of visibility. However, it's extremely slow. It's fastest speed is still slower than the Seamoth and you can't use it for more than 15 seconds without catching on fire. It's also just too big, and kind of annoying to maneuver around. It also drains batteries like mad until you put a couple efficiency upgrades on it and there's no convenient method of charging it at your base. You have to constantly be swapping out batteries. Would have also been nice if it had room for both the other vehicles so you didn't have to constantly go back to you base to swap.
The Prawn Suit just sucks. It feels awful. You are slow and heavy and you can't see crap. You are stuck to the sea floor and can only look up about 45 degrees. You get this piddly little jetpack jump that is completely useless without the upgrade and a very short suction cup line so you can drag yourself up a wall with your face grinding right into it. I also didn't find the other half of the drill arm until I had basically crafted everything already so I hardly got any use out of it.
The game also is in serious need of a map. I didn't realize that I had already been everywhere and spent about 2 hours searching for a new biome or cave entrance that would lead me into the deeper waters I knew existed because of the depth upgrades. After giving up and consulting Google, it turned out the entrance was in a cave I'd already been in and didn't see because I was exploring it in the prawn suit and had already found an alien research station and concluded that was the extent of the mysteries within.
The survival mechanics were vestigial at best. There was never a moment that I was ever in danger of not having enough food or water. Storage also kind of sucks. Once you start base building building additional storage is dirt cheap so why are the lockers so minuscule? Just let me dump everything in one or two sorted lockers so I don't have to remember which of my 15 shelves I put the copper on.
Also, why the heck do they let you dive underneath the level? Several times in my exploration I noticed extremely sharp drop offs full of monsters that are very deep. So of course I concluded that this was an endgame content location. After getting the second depth upgrade for the cyclops I decided to see if I could reach the bottom. It took several attempts and many decoys to get past the leviathans, but I finally made it to the point that the level just ended and you could clearly see all the flat walls surrounding the various bits of the world and could tell that the deeper bits were more toward the center. It really killed the immersion for me, and was a disappointment on the whole. If it's the end of the level they should just not let you dive any further. Just say that a mysterious current is pushing you back upwards, or make it too deep to dive to even with max upgrades. As it is it's not really clear and it seems mysterious. I also don't understand why you can't see the islands from the surface of the water, they are obscured by really wispy looking clouds for... reasons.
I did like the game. Really, I did. But there was just a lot of annoying janky bits and I was kind of sick of it by the end.