EDIT:
I just spent the last 1.5 hours playing Reus. Cool game!
You are the planet and control different giants that can do different things. You have a rock/mountain giant who can make mountains that create deserts and he can also create patches of minerals to give wealth to settlers that move into your areas. Forest giant creates forests, fruit, and animals and can increase fertility in areas. Swamp giant for swamps and can create animals and food and other things, and the Ocean giant for oceans, monsoons, and animals. Each giant has like 7 different abilities but only a few are unlocked at the start. You gain more by helping the humans that settle your various areas (forest, swamps, desert) by providing resources they need to complete their projects (granary, shrine, school, etc). When you help them finish one of these projects in the time limit they provide you with an ambassador that rides on your giant. You pick which giant the ambassador will ride on and depending on the giant the ambassador will unlock a new ability for it.
Sometimes the human settlements become to unruly and rage war on another one for whatever reason (resources, hookers, blow, etc) and you can use your giants to destroy their settlement and save the other one if you want.
Pretty neat game, there is a lot of depth to it because everything can be upgraded and building some stuff next to other stuff creates symbiosis which will increase whatever the two things do and can upgrade an item to do more. An example from the tutorial, use you the forest giant to grow fruit, the fruit is blueberries as its base, use the ocean giant to have animals created next to it, they are chickens, now the chickens feed better and you gain more food because of it. Then you can use of the giants fertility/grow abilities to upgrade the blueberries to tomatoes and that increases food production more and gives you some technology as well now.
A lot to it when you have 4 giants and various different things but it is cool. If you dig the whole god genre thing I recommend it.