I'm gonna fudge this a little and say Street Fighter III, which is a few months out from being 20 years old. To the best of my knowledge, the spritework for the game wasn't really updated in the translation to its console port, meaning that the stuff released in the original arcade cabinet is as it was almost 20 years ago, and some of it is just remarkable.
http://www.zweifuss.ca/index.htm
This, and Sonic 3 & Knuckles.