Amiga:
32 color graphics, with certain objects left out from the PC version (though an odd one was added, like the fish in the woodsmith's shop which is not in the PC version). Better music quality than the PC version. A lot of the tracks were left
out though.
Mac: 256 color pseudo-anti-aliased graphics, and better music quality than the PC version.
You are currently reading the old section of The SCUMM Bar. With Monkey Island 5 --
Tales of Monkey Island -- and The Secret of Monkey Island: Special Edition
announced, you probably want to check out
the main part of the site.