Shadow of the Beast may be the definitive Amiga
game, with beautiful graphics and sound (by David Whittaker
of Lazy Jones fame, no less) and a very high difficulty
level.
While primarily an arcade game, Beast does feature
some puzzle elements (i.e. find item before killing boss,
etc.) While you could call the game a graphics demo with
a game attached, I feel it goes one step further. The
graphics and sound are more than technical achievements,
i would truly call them art, and they set up a mood for
a game that i have yet to see matched even today.