I have many ideas about that topic but first i like to show a basic think about seasons.
Like everyone know we have a four seasons in the year then i must to say something about all of that:
All differeces betweend spirng and summer will be in special plants. Spring is not that hot season like summer then u cannot plant everythink u want. Example strawberries or tomatoes need highes temperature to grow up. Then in spring u can plant: carrots, beans, pumpkins, potatoes, apples tree, radish etc.
In Spring and summer game graphic will be similar without any big changes. Difference betweend Spring and summer will be on plants and different kinds whot u can find in forest like blueberries, blackberies and spices.
People who live in central europe know how real autumn looks. Leafs on trees change colors from green to yellow and red. In forest u can find except all that from spring and summer mushrooms.
Winter ( is coming !)
The hardest part of year. Trees without leafs will be stay on the snow floor. Hungry animals will be much more agressive. Like we know winter is cold and we cannot plant any wegetables and fruits outdor. In buildings craft will be an option to build a greenhouse. Walking on the snow will be much slower without special snow rackets. All lakes it's turn to big ice cubes. People without special clothes will be lose HP from cold.
This is only basic thing about seasons, i focus on simle differents between parts of year. I have an more ideas about this but i don't want to mess up in you minds :P
Sorry for my english, usually I don't write posts in this language :P If someone don't understand what i say here i try to explain it again in easier way. If u have any ideas how to improve that will be great.