I have been thinking lately in doing something which I can build upon and won´t be a crazy big concept from the very start. Cartoony post-apoc dude who lives in a city, right in the middle of mountains of trash, think of Deponia (very fun graphic adventures).
You are a scavenger and find a blueprint for a wind generator while sorting trash, build many of it with neccessary scavended pieces, sell energy to city, improve generator with money, scavenge more zones, find more energy generation methods. Go clean or go dirty (trash burners generators vs plant trees, make anti-trash walls...) and in the end reap what you sow.
First person, simple combat (critters among the trash in need of a whack on the head), a bit of automation. Latter suprising the player by making them worry about their generators not exploding by lack of cooling...
I know for sure I would have fun making the 3d models, not so much for the coding.
Is it available somewhere?