I'd also like to highlight Modern Chemical Plant's design. The immediately branching paths at the beginning are really clever (for both rewarding different levels of player skill and making a lot of sense in the environment), and the level is peppered with a lot of minor shortcuts and room for improvement on subsequent playthroughs. From a spectacle standpoint, free falling down the giant vat of the bubbling blue chemicals is impressive, and running through the zone as it falls apart is a neat twist (even if it goes a bit over the top with explosions at the end).
Heck, if I didn't strongly dislike the way the kart handled, I'd probably feel like heaping some praise on Modern Seaside Hill, too. There's a lot to love in Generations, even if it has a handful of glaring flaws.