What you're looking for is called a "Vertical Slice" in games. The systems you intend to build done as mocks or stubs, used to convey the overall sense a game is meant to convey. You have to build a lot, but it serves the same purpose of checking to see if people actually like a game/its mechanics. Also, in a vertical slice, you can use unpolished game assets or just graybox everything. The point is the "feel", not necessarily any individual look or mechanic.