Casper as a character is instantly recognisable to me, yet the only Casper thing I think I’ve seen is the 1995 live action film. Still, you don’t need to know much for the game: Casper is a friendly ghost, and in Spirit Dimensions, he’s tasked with saving the spirit world from the evil Kibosh. While it’s structured much like a 3D platformer, it’s a flight-based shooter.
When I did research on Casper: Spirit Dimensions, one thing that came up a lot was the frustrating dual stick control scheme. For the GameCube version, it seems like the developers listened to the complaints and simplified it for GameCube, as instead of moving forwards/backwards with the right stick, you now use L to accelerate (and one of the options lets you use the full click to activate Casper’s turbo).
When you lock onto a target, the controls change to allow you to move up and down and strafe. and Casper fires blasts of energy from his hands. You can collect fire and ice power-ups, or collect energy that can let you either fire a charged attack or go invisible, which protects you and lets you fly through bars (despite being a ghost, you can’t go through walls, which is odd but a reasonable limitation for a game).
But there’s really not a lot to Spirit Dimensions, as most levels are aimlessly flying around looking for objects – even though it’s a very short game, it still drags on. One odd quirk I noticed with the levels (of which there are four, with a few sub-sections) is that some sections have platforms or ramps, as though the game was going to be a traditional 3D platformer at some point. Even the final boss’s level has a gorge for flying into to collect power-ups, and it has a ramp to climb up, even though you can only fly.