Try keeping it simple. Old 8-bit adventures had very simple art that were essentially vector art. You can simulate the style of art quite easily, and churn through the pictures.
If you are not a natural artist (as I am not), it's certainly worth going the abstract art route. See the graphics in Escape From Dinosaur Island DX (not the loading screen), as an example of how to do abstract style graphics.
Or ... an artist can step forward. :-)