I've always found the EGA artwork in LOOM and Secret of Monkey Island to be very impressive, particularly the artists' use of dithering. But the art in those games was mostly static backdrops, so it wasn't very CPU demanding at all.
I used to play F-29 Retaliator on a 286 with VGA and it was doing surprisingly good realtime 3D rendering. Didn't feel sluggish at all. I've seen comments that claim this was actually an EGA game, and that its speed came from using graphics write mode 2, which let the game write a solid colour fill to 8 pixels at a time. (When I get my RGBI monitor fixed I want to see if it really does run on EGA and if so, how fast it plays on a V20 at 10mhz.)