Of the three "Falls" at Typhoon Lagoon, this is the longest and zaniest. Don't think it's an intense slide with long drops and lots of screaming - it's pretty darn tame. But nonetheless, it's a spirited good time.
Note: unlike Gangplank Falls, Mayday is one-person tubes and has some sharp turns. And unlike both Gangplank and Keelhaul, Mayday requires lots of walking up to the top of the mountain - stairs, stairs, and more stairs - so enjoy the ride down!