I can't really say that I have an all-time favourite, considering I easily shift my interests and I may at times prefer that one game over the other or vice versa.
Recently though, I have been extremely impressed by an early-access game which is
Subnautica
I am an extreme fanatic when it comes to exploration and diving. This game offers a lot in regarding in those aspects, the idea that you're diving in an alien ocean is just extremely fascinating. The thrill when you go deeper and deeper into the unknown blue and discovering things that you've never seen before. If you're the type to appreciate landscapes as well, Subnautica offers a lot of those aspects. How the flora and fauna in the game is absolutely stunning in terms of appearance and behaviour. How the structure, content and landscape of that game really share their similarities with our real life ocean counterparts such as underwater caves, trenches, plains and many other sort of ocean geographical similarities. Beautiful but deadly.
From a technical aspect, for such a game with well-done graphics, you don't really need a powerful computer to run it. Well optimized, especially in the recent updates. Its UI, mechanisms and interface are extremely convenient and simple unlike a number of other survival games. How the game actually has a story and a plot which you can choose to follow or not but it does lay out a more a big appeal. The fact that the game is early access and there are still a number of updates still coming in excites me.
Gonna use this quote on here. This game has more depth than many other survival games out there. Literally as well.