I’m making some test art assets to fill out the game world and give some basic components to hang gameplay on. So far this consists of a few buildings, some GUI components and an animated character. Stage 2 will be getting the gameplay tied in to the art so the core gameplay works.
I know other people like to start with bare bones no-art prototypes, but for me the art is as much a part of the game world as the backstory, combat logic and the upgrade paths – ie: Fundamental.