The best thing about Slime Rancher's [official site] trailer is the sound effects. Lots of "wheeee!" and "haha!" and gloopy landing noises. On the auditory cuteness spectrum I would put it somewhere between Loco Roco and Yoshi Touch & Go.
As per the developers:
Slime Rancher is the tale of Beatrix LeBeau, a plucky, young rancher who sets out for a life a thousand light years away from Earth on the ‘Far, Far Range’ where she tries her hand at making a living wrangling slimes. With a can-do attitude, plenty of grit, and her trusty vacpack, Beatrix attempts to stake a claim, amass a fortune, and avoid the continual peril that looms from the rolling, jiggling avalanche of slimes around every corner!
The game revolves around sucking and blowing things with your vacpack. That includes food harvesting, collecting and corralling slimes, and, I think, weaponising them.
I've had a little poke about on the dev blog and there are a whole lot of different kinds of slime with a whole lot of different dietary requirements. I'd assume the balloony pink ones are the basic/beginner type but there are rock slimes which have spikes on their heads and only eat fruit and irradiated slimes which cause radiation sickness but can act as batteries and eat vegetables.
The slimes produce "plorts" which is why I was ready the dev blog - to find out what a plort was. They're concentrated balls of slime which can be used to produce different resources. As far as I can tell, this is another way of saying that it's valuable poop that you sell to corporations so they can build starships and all manner of other things.
The game is expected to launch in 2016.