omg it's Splashdown
I think this pack strikes a really nice balance between creating solid race-courses, and introducing little twists to keep things interesting.
While the difficulty varies, readability is almost always crystal clear, so even the more technical maps don't feel unfair.
Other than being consistently fun, the thing these maps all have in common is strong, yet simple visuals. Texture variety is limited, and sector art isn't overly complicated, which results in really clean looking, appealing locations. Even if you're being mauled to death by motobugs, or set on fire - these maps are nice places to be.