I might split it up into two approaches. If you want to simplify walls/obstacles/buoys into one category of turn, that seems like an input-based approach - where holding right on the stick is holding right on the stick regardless of the associated freedom/challenge. It might lead to a discussion about "what is the solution to this course?". Looking at elements like wave size and their effect on the player seems like it would lead more to "what is the challenge of this course?". Kinda a high-level versus low-level thing? Maybe that's just me. Anyway, I'd break down the elements like this:
From an input-based perspective, maybe it could be:
- Forced turns, which prevent an incorrect steering input (composition of walls and obstacles)
- Bonus turns, which reward a correct steering input (the right side of yellow/red buoys)
- Jumps, which punish (but rarely prevent) an incorrect steering and/or acceleration input
- Waves, which reward a correct traction input
Basically, what contexts inform the translation of player inputs into speed.
Whereas an element-based perspective might take into account:
- Walls
- Boundaries (those outer buoy lines that you can only stay outside of for 5 seconds)
- Buoys
- Ramps
- Low surfaces (that you can ride over but lose handling/accerlation)
- Waves
- Turbulence
- Spike balls (these behave slightly differently than walls since they immediately knock you off no matter what your angle of approach)
- Ice bergs can kinda fit in with spike balls
- The placement and size of all these objects
I guess maybe composing those elements and their interaction seems like a lead-in to the higher level input-based comparison.