I've been following this game for a very long time. I was a member of these forums since very early on. Slime Rancher has always been special to me because of the cuteness and just the pure fun that can be derived from the game itself. I've played 12 hours on the newest patch after not playing the game since 0.3, so I think I'm ready to provide some feedback.
And please, I love this game. Don't vehemently or rudely disagree with the things I say. These are my experiences. I like the game and I want it to succeed and it's not like I played it for 20 minutes and dropped it to come here to complain. I put 12 hours on the latest patch.
First off, I feel like after a certain point, the game just becomes work. And not the kind where you get to enjoy the fruits of your labors either. It feels like work for the sake of work. At first it was extremely enjoyable, but the more you expand your ranch (which is something you should be ENCOURAGED to do) the more difficult the game becomes. Now, this wouldn't INHERENTLY be a bad thing, but it doesn't get difficult in a healthy way. It doesn't get challenging in a fun way. It gets stressful. There's so many things you have to maintain that it gets ridiculous; I get stuck on the ranch for half an hour longer than I was planning because there was just so many things I had to take care of. The autofeeders and autocollectors do alleviate the pain somewhat, and too much automation would completely ruin the point of the game, but there's something definitely missing here. I would suggest hiring caretakers that are paid by newbucks, but that would be complicated to implement. It would require AI, modeling, animating, etc.
I'm sorry this is feedback so nebulous as I cannot suggest something concrete, but I think it's better this way, because the devs get to think of their own solutions. Sometimes it's better to be presented with a problem and not be shown the way to fix it, if you have the ability to fix it yourself. It's good to be able to do your own thing.
All I know is that I was only playing the game because the cuteness kept me there. It turned into work, and I could no longer implant my heart into it. Sure you can suggest things like "just reduce the size of your ranch, release some slimes into the wild if you find it hard to take care of them, etc" but to me, that defeats the point of the game. I want to have many, but I also want to have the tools necessary to take care of them all.
I can make some very loose suggestions. Maybe an upgrade to connect a corral to a crop so that the crop sends food into the auto-feeder through a tube? Or if that's going to obstruct the map too much, maybe have the food teleport into the autofeeder instead. Then you just have to worry about keeping the crop full. There is still gameplay on the player's part, but just a lot less stress and a lot less things to think about. This, I believe, won't ruin the point of the game. There are some slimes that I prefer to allow to roam free, and others I want to keep in a corral where their side effects are controlled and they are kept safe, like Rad slimes and Boom slimes. I think it's totally okay that you have to hand-feed the free roaming slimes, but if I have slimes in a corral, I want to at least have an upgrade that allows me to automate their autofeeder, or have an AI rancher take care of their autofeeders (in return for payment.) I understand that the more you grow your ranch, the more you need to pay attention to it and care for it and the less time you have for exploration, but you need at least SOME time to explore. The way my game is right now, I can't leave my ranch without KNOWING that I left something untouched but thought "it has to wait, I need to explore for stuff." One primary facet of the game should not punish you for playing the other primary facet of the game. And my ranch isn't even that insane. I have two corrals of Rad Boom slimes and two corrals of Pink Rock slimes. I have Tabby Luminous slimes in the cave, where they are kept permanently fed by the Cuberry trees I planted there, and Tabby Honeys in the Overgrowth where they are permanently fed by my coop and the chickens that inherently respawn there. It really doesn't sound like much, but I'm running all over the place making sure everything is full. I don't have enough locations for enough crops to be able to fill the autofeeders enough to have peace of mind when I leave. I have FOUR crops of Oca (because it grows much more slowly than other food) and THREE crops of Heartbeet (because I have a lot of Pink Rock slimes to feed.) And speaking of feeding, is there any possibility of adding an upgrade to increase the size of a corral? Because my Pink Rock slimes tend to bounce around on top of each other and cannot get to the floor to eat the Heartbeet that my Autofeeder shoots out, which gives me another thing to worry about. Perhaps make it so the autofeeder shoots the food from all around inside the corral rather than from a single point?
Also, this last one isn't really feedback but instead just an idea. I also suggested it a long time ago back when I was new here. I'd really like the ability to pet the slimes, just for the heck of it. Maybe give it minor effects like increasing their happiness, and if you really want to spice it up, make each slime have unique petting animations. I got this idea the first time a Tabby slime jumped on me; every fiber of my being was saying PET THE SLIMEKITTY! There are many ways that the slimes can interact with us, so how about us being able to interact with them? Surely Beatrix does not view these creatures as mere money bags? Well I guess some of us do, but the petting function won't be for those people :P
Slime Science is fun, although plort costs are just a little bit steep. Just a LITTLE bit. A 10% reduction on everything should be okay. This will not be necessary though if ranching was made a bit less stressful, thus allowing for more slimes and thus being able to fulfill the costs better.