Subnautica
An astonishingly good single-player survival sandbox game that weaves the familiar mining-and-crafting loop into a very satisfying story. Unlike many games in this genre it does not use procedural world generation, allowing an experience that is carefully designed for progress and balance. This does limit replayability, but then there is a sequel (at least one at the time of this review), and a sandbox mode that can go on forever.
The highlight is the world itself. It's beautiful and diverse and reveals itself to you slowly with many delightful surprises along the way. Most of it is underwater (duh) with a really nice control scheme (except for one awful transport). It's like flying but better: fluid and flexible and yet carefully controllable: there are almost no currents. Though motion is a bit slow, the game world is not so big as to make it too tedious and you get upgrades later on that improve the experience of exploring.
The save system is simple and excellent. You have only one save slot and no auto save. (Unfortunately it doesn't tell you that. I lost a couple of hours in my first playthrough because I did not manually save...) This introduces real risk while giving you choice about the punishment. Let's say you save just before doing something dangerous or experimental. After 30 minutes you die and are respawned at your last base (possibly very far away) and lose some rare materials. Now you can choose: do you continue playing and accept the consequences or reload the last save and forego 30 minutes of progress? Too many games force only one path.
Subnautica does not hold your hand much but in the early game offers you something of a guided tour. Once this tour ends, however, things quickly become quite obscure. It's easy to miss little items and hints, in which case you will just have to revisit all locations and scour again and again. This can be frustrating as is evident by many online posts about not knowing what to do next. Luckily, the community is good at giving gentle hints without spoilers, but this aspect is the game's weakest. It's compounded by your visibility often being very constrained, which is amazing for atmosphere but awkward for gameplay. I wish there was an option to at least tell you if there were still undiscovered hints nearby, to reduce frustration at the cost of immersion.
On the other hand, another instance of deliberate obscurity is actually fun: the lack of an in-game map. You need to instead rely on navigation devices as well as your own sense of direction. This adds a lot to the atmosphere and forces you to become viscerally familiar with the geography and the journey.
As is common for this genre, there are many little and sometimes important things the game doesn't teach you about movement, item use, crafting, building, etc. Again, online guides come to the rescue. Finally and unfortunately, I did hit an annoying bug a few times. Luckily, the cheat console allows you to work around anything.
My big wish now is for a multi-player game from this team. Though the community has created a multi-player mod for Subnautica, I think it would be a poor fit for game's design, story, and atmosphere, which are all about being stranded alone in an alien world. We would need a new game with a new design. Please make this happen!