Ark and The Forest also caught my eye, but I ignored them.
I thought I'd post my tuppence on those games for you....
Ark. No. Just no. Ark is a PvP game at heart, and best played with a clan of your buddies (and if you do this it is excellent). However, playing Ark solo, whether PvE or PvP, is not a good experience, trust me. And Ark PvE in general is lame and verges on pointless.
The Forest. Is absolutely fantastic, and one of the most frightening games I have ever played. I do not want to spoil anything about it for you, it is 100% best played knowing nothing but I highly recommend it. The atmosphere and sheer terror it creates has to be experienced. If you asked me a few months ago, I would have rated The Forest as the 2nd best survival game for solo PvE, just after 7 Days to Die. However, now that A17 has landed, my opinion has absolutely changed....they are both 10/10 games, but The Forest is the better game of the two now (just).
And as for other survival games, I have sunk a decent amount of time into all of these....
- Subnautica: It's OK, but really suffers from being single player and has zero replayability. Painful grind near the start (sound familiar??) [6/10]
- The Long Dark: Great but very serious and pretty hard. [8/10]
- Don't Starve: Simply fantastic. Can't recommend this one enough. Especially with friends. [9.5/10]
- Raft: really really fun and very mellow but lacks content. About 10 hours of joy and zero replayability. [8/10]
- Flame in the Flood: Again, superb game, more depth than Raft, but not great replayability. You'll get 30 to 40 hours out of it. Stunning cartoon style graphics though, really beautiful. [9/10]
- Frostpunk: Beautiful game. I would have said lack replayability because it it scenario driven, but they recently added an endless sandbox mode which I have yet to try. [7/10]
Sheltered: Team 17's fabby side-scrolling pixel-graphics nuclear bunker survival game. Very addictive and simple to play, but offers a great deal of replayability. [8/10]