Splashdown: Rides Gone Wild is a pretty fun PS2 game. It has large outdoor fantasy "world courses" based on amusement park rides. The "stadium courses" are indoors, but also fantasy-based. However, the game does have more realistic courses for the "technical time trial" section.
For a game with such simple controls -- steering and gas are the only inputs other than doing tricks -- it has a lot of replayability. It has very convincing (though fantastic) physics including many different types of waves.
The best way to quickly progress in the game and unlock more content is to start by unlocking one of the faster hidden characters. Jonah has good top speed but his poor acceleration makes him difficult to use. Probably the best character to unlock first is "Wrong Way" McNabb. He has good speed and acceleration, and once you have him you will have an easier time winning the seasons and unlocking more.
The very fastest character is Agent Michael Hawke, who is a 007 type. With any of the extra fast unlockable characters, including McNabb, it becomes possible to "overshoot" some of the jumps and crash into walls or miss turns. With these characters you sometimes will need to slow down just before a jump.
I like the look of Coral, but I did not find her to be as easy to race as McNabb. Coral does have funny audio clips though, including one where she says, "fo' shizzle my nizzle."
At first I did not realize the importance of unlocking other characters, and I spent a lot of points on alternate outfits for Kyoko. She is a pretty useful character for the Freestyle competition, though.