A good mix of no-nonsense and more experimental race maps.
Generally very visually appealing (except Sleeping Egg imo, kart struggles to render dithering nicely), with strong theming.
The heavy use of spring panels on some maps might be hit or miss, depending on who you ask, but I find it brings a nice change of pace to netgames
Nightmare Pack is one of the earliest and most respected map packs I can think of. It's full of fun and memorable layouts that work to Kart's strengths. Each one is really varied in theme, and this pack features maps of high and low difficulty for new and old players alike.
Some of the most memorable tracks have to be Hadal Trench, whose latest iteration is a long, winding adventure of a map down to literal rock bottom; I always appreciate a good spongebob reference. Sleeping Egg and Lazy Summit are both old maps with a totally new coat of paint, both featuring adjusted layouts and new textures. Nintensis has mustered the willpower to go over all his older maps in this fashion; You won't find any old crusty maps here.