I think giving each area it's own art style could be kind of neat but also having mixed art styles could be pretty cool too

Yeah :) I'm still trying to work it out, but the way I have it now is each "world" has a more general over-arcing theme to it (Like "industrial" or "scary"), but each individual level will lean toward a specific method of animation/style, such as stop motion animation, old Soviet era animation, etc.