Any game by Sierra Online. They didn't bother to improve upon the lame PC (EGA? CGA? what gives) graphics.
They seem to have thought that porting to another system meant only utilizing the lowest common denominator of all systems the game is available on; the original PC version in their case. Since they originally made it for the PC, they deemed it unnecessary to actually figure out how to make it multiple times of magnitude better with the Amiga's capabilities.