Well, so far I'd have to say this game is both really good and pretty bad at the same time. But the good thing is the bad stuff is easily mitigated once you understand it. But the game does a poor job explaining it. If the game was better able to make its intentions clear during the opening sequences, I think people would have responded to it in a better way.
As I see it right now, the game isn't about consistent progression, as many other games are. On the micro-level progression, it's about living in one place for a long time, venturing out each day to find food, then going home at night to rest. Basically, it's about the day in, day out of life as an animal. On the mid-level progression, it's about extending your knowledge of said place, and your ability to travel further before going home. This gives you more map to work with, helps you know where various food sources are so you can find food if one area has respawned its food that day, lets you know where the dangerous enemies will likely be (though that won't be perfect due to their AI), and give you various points of interest. And then you have max-level progression of getting back to your family, as set up by the intro. This is great stuff. It gives the game unique atmosphere, tension, progression, reward system, etc. It makes you feel like an animal, which is important.
The problem is the game doesn't properly condition the player early on to play the game as (I assume) is intended. I didn't even come to these realizations until checking this thread and learning about rank. If the ranking system is going to remain in its current form (and I'd imagine it would because the game is out, and changing something so major probably wouldn't be a good idea), then any updates to game need to find a way to make it clear to the player what rank is and why it's important. Because even though rank is an abstract, and it doesn't make sense that it can physically affect the world the developers built, the necessity of rank and the time limit of rain are the core pillars that support the foundation of the game's "a day in the life of an animal" progression. And that foundation is fundamental to what makes the game so unique, so something needs to be done to keep the foundation without losing players after a few hours.
A few things they could do:
1. Put the player in a position where they have to open a rank door almost immediately. You've got your little hologram buddy, he's leading you around. Have the first two or three rooms be a linear path that leads the player to a door that doesn't open because they aren't the right rank. Then have the hologram buddy lead the player to shelter to sleep, then the player ranks up, is lead back to the door, then the door opens. Make it something the cannot miss. Then when they come across another door, they'll know what to do.
2. Make the rank up animation more easily noticeable and unskippable (at least the first few times). Correct me if I'm wrong, but I'm pretty sure once you go to sleep you can just immediately hit continue or exit without watching the full animation. I'm pretty sure this is what I did, because I saw the slugcat picture, thought "that's cute" then hit continue and never noticed the the symbols on the left side were doing something. Slap that animation right in the middle of the screen, force players to watch it go up or down, whether via rest or death, then allow them to continue. That way when players get to a door, and see the symbols on/around it, they have a greater knowledge of what those symbols are.
3. I don't really like this next suggestion, but obviously, you can just tell the player what it is. Personally, I think finding a natural way to explain without text is better, but you do have text that pops up telling the player exactly what to do with other stuff like rain and food, so doing that with rank wouldn't be out of the question. But like I said, natural solutions are better than abstract ones.
Now, all that said, I must say I'm disappointed that the game released with the current ranking system in place at all. It doesn't make sense in the game world and I'm confident you guys could have come up with a better solution. But like you said, I'm sure you needed the game to come out eventually since you'd been working on it for so long, so I can understand if some things don't end up so great. It makes sense for there to be a ranking system of some sort, but not for it to be tied to opening doors in the environment. It doesn't make sense for these gates to act like bouncers, and only let me into their club if they think I'm cool enough. It would've been better if you rank simply affected other creatures. Like making certain lizards more aggressive because they think you're weak, but then they get less aggressive the more they learn how tough you are. Or certain animals befriend you once they learn you aren't a threat. Maybe all that's in the game already, I don't know. Point is that's all it should have been.
If you wanted to gate new areas, I think a traditional lock and key system would have worked much better. Because the world is harsh enough, and you already have the rain keeping you from progressing too far too fast, you could still achieve the "live like an animal" goal with a more traditional structure. Something like each gate to a new area requires a certain number of nodes to be found and activated in the world in order to unlock the gates. You have to explore the environment (the mid-level progression mentioned earlier), and you still have to go back and hibernate and maintain your food level and rank up (micro-progression) because the uncharted territory, the enemies, and the rain simply will not allow you to gun it to each node as quickly as possible. Hell, you could even make it so that the nodes were little glowing balls that the player had to carry them back to hibernation spots, because each hibernation spot has a little tube that carries the ball to the gate to help unlock it. Then, even if the player was fast enough to find nodes too quickly, they would only be able to carry two at a time. Theoretically, this type of system would maintain the fundamentals of the game, while being far less abstract and difficult to understand.
But still, the ranking system does do its job. And the progression of the game is really unique and interesting. It's just a shame that many people will have to go online and learn that it even exists before it will do its job properly, and many people won't even do that and will just drop the game. Because I've been having a great time now that I know about this stuff. Hopefully other people will too.