Kyouka has 12 hours each day to go outside and scavenge/explore, but this gameplay element is actually completely unimportant, almost entirely unconnected to the main story, and tedious. For example, if you work hard gathering a bunch of materials across Akihabara (while holding down the sprint button because version 1.0 of this game doesn't have an auto-run setting), you may be able to cook something which will give you a bonus effect the next day. That bonus is usually something like 'you will gather 1.1x as many vegetables' or 'searching for materials will take 0.9x as long'. Not only are the bonuses very weak, they're unnecessary in the first place, because you have infinite days! Who cares about saving 10% of time the next day? Does searching a shop for materials taking 27 minutes instead of 30 minutes out of your daily 12 hours feel like that much of an accomplishment when you have infinite days? And at any rate, when you progress past certain chapter milestones, the day moves onward on its own (and the next day you have no food modifiers). You can easily complete nearly every story event within the 12 hours of one day cycle to move to the next milestone, so doing the survival gathering stuff actually slows you down! Starvation is also not an issue since you start with 270ish servings of cup ramen even if you somehow need them, and even if you don't eat anything, I don't think you can ever starve (I tried having them not eat anything for many days in a row and the only downside was a 'hungry' debuff that made gathering take 2x as much time).
It's a very odd system, it's almost like they realized that running around Akiba scavenging materials wasn't fun enough to add gameplay checkpoints for (i.e. they could have added some chapters where you have to stop and spend a few weeks scavenging for materials in order to make the gameplay relevant to the story), but couldn't bring themselves to remove it entirely, so it's just...there. It's there if you want to get the cooking and hunting-trap trophies. You can gather tungsten wire and a bunch of other stuff and make fancy traps to lay around and then go harvest meat later to cook, which will...give you a small bonus to your gathering the next day. It doesn't save you any time or have any strong connection to the story. The story is instead progressed by moving from shining beacon to shining beacon on the map to trigger the next VN section. Occasionally you have to craft something, but in the rare case the game doesn't guide you directly to the ingredients for it, they are easily gatherable in a few minutes. You can pick two characters to go outside with you and they'll have a few lines to say each chapter, but that's about it for the field gameplay.
Again, it's hard for me to compare this to other yuri VNs because I just simply haven't played any others (I'm the type who usually needs at least some gameplay to pick up something). But, I suspect most VNs that mainly focus on romance (of any kind) are very drama heavy. To All of Mankind is not just about romance though, so it's light on the drama - it certainly exists, but it's not too heavy. It's mostly lighthearted, and it's all in the context of a group of friends who do their best cheerfully working together to survive in Akihabara. The three main themes are the relationships between the characters, the survival lifestyle aspect of them finding ways to make do with what they can find in the ruined city, and the lingering mysterious aspects of the story (why were their memories hazy? What happened to everyone else? What exactly is going on?).
I don't really have good comparisons to make about the story, i.e. to say that I liked it 'better than X, but not as much as Y', so all I can say is that I thought it was 'good'. Not amazing, not bad, but good. I know, I'm sorry, it's not a very useful assessment, is it?! I told you I was unqualified for this. Well, I'll try: It's mostly lighthearted at first but tension and mystery builds up over the story making you want to learn more, the character interactions are fun (if a little cheesy at times), and the survival shenanigans are entertaining. The game is almost entirely fully voiced (I'd say about 95% of main story lines are voiced, with some unvoiced conversations on the field and when you cook things).
My first playthrough took me about 15-18 hours I would guess, although it would have been shorter if I had skipped the survival gameplay stuff, or a bit longer if I had gone for the hunting or cooking trophies. I fished and trapped a bit and made sure my characters ate well most days, even though it didn't feel necessary.
Playing a second time with Shuka adds a surprising amount of story. Your first playthrough has some parts where Kyouka feels very sad about something she can't quite understand, openly muses about how she really feels like she's forgetting something important, has the characters find something in Cyrillic with nobody who can read it, etc. all dangling loose plot threads to entice you into playing a second time with Shuka to tie up the loose ends.
I liked Shuka, but it was a tad annoying at times how she overlapped with Yuyuko's character as the 'genius' of the group at times. In the first playthrough, Yuyuko is the one who is the big brain of the group, but this time around Shuka does a lot of the things that Yuyuko would have done instead. Still, it's a minor complaint, and she adds her own flavor to things in other ways. More importantly, the plot actually diverges hugely near the end if Shuka is in your party vs your first playthrough: the last two chapters are entirely different and the endings are also very different.
Anyway, Shuka's DLC is mandatory in my opinion if you want to say you actually played the game ('read the VN'?). The second playthrough with her in it, assuming you skip all the text that is identical to the first game, is another good 10 hours or so of content that ties up a lot of hanging plot threads, making To All of Mankind around 25-ish hours in total, again, adjusted a bit up or down depending on how much of the gathering/cooking minigame stuff you do.