As far as I've understood it, there was really only one prominent pixel artist in the 2600 scene: Jerome Domurat. His work is pretty cool. Check out this background from E.T.
Given the system limitations, it's at least above par for creativity for that time. Of course, people working in the scene now are coming up with far more impressive art, just because they're coming into it with a far more developed understanding of the fundamentals of pixel art.
- Adam
