Whats good about shadowgates graphics are the free flowing hand painted look, no repeating tiles, the highest number of background colors in a pc engine game and the most heavily use of color for shading Ive seen in a game with 16 bit graphics, for example the skull with the sword sticking out of it in the first screenshot i posted has 44 colors in it alone.
Whats bad is....imagine taking 44 colors of the pc engines palette and spreading it across a sheet of paper your going to get all kinds of colors which is what gives it that dithered look so you don't get that clean sharp look that are in games like rondo of blood or winds of thunder.