Commander Keen's adaptive tile refresh
The fluidity of the scrolling in Commander Keen 4-6 was unmatched on PC for years, even as games moved to 256-color graphics. Between Carmack's incredible technical work and Adrian Carmack's [1] art, Id had perhaps the best-looking PC platformer well into the 1990s.[1] No relation to the more famous Carmack, but IMO the unsung master of the 16-color palette.