The idea of the game is to work on good runs through each circuit for each stage, which is why you're scored on each and get a leaderboard at the end. Collecting items, going through rings and killing enemies all give you points, and you gain multipliers based on how many you can link together. What you should be doing after destroying the cage thing is to keep running the circuit for as much time as you have available to get a high score, then continuing to the next part. Brad was getting low grades because he wasn't doing anything to raise his score, and you can't complete the game with this approach because you need a C or better on all the stages to unlock the last one. I think it's fair to say this is an arcade game that never saw release in the arcades. The levels are pretty short and there's seven in total, but they get pretty intricate, so you're intended to play them over and over to work out a perfect line.
There's a lot of other stuff, like the proto-Chao system, but I've never really understood how that works. Also, there are little touches like making the music change dynamically based on how you're playing.
This is what ridiculously high level Nights looks like, but you don't need to take it this far to be able to finish the game or get As on the courses.
