Don't Starve has a very unique art style, using two dimensional or 2d characters and items in a 3d world gives a very interesting artsy feel to the game. The hand drawn look and feel to the graphics are a nice change of pace from ultra realistic games, but it doesnt take away from the suspense.
With randomly generated (customizable) levels, different characters, ever-unfolding story elements, and permadeath, the game offers a lot of variety within the goal of constantly striving to survive longer.
A lot of survival games focus on the basics of survival. ARK takes that further, giving players longer-term goals, like taming dinosaurs, which is way more interesting than just needing to eat or find fresh water.
Since the player is stuck underwater for most of the game, things like hunting and resource gathering are completely different from other, more traditional survival games. You're never going to build an axe to chop trees to build fires here, folks. The game's underwater setting means that...
Subnautica is quite possibly the most frequently-updated Early Access game on Steam. Each major update includes significant improvements and fixes, to the point where it's always fun to dive back in after an update.