I feel like Ross nailed some of my experience game. There's a lot of personality and good here, and a lot of, for a lack of a better term, jank. I played the actual gamecube game and later the pc and I can confirm what was said in passing earlier, the PC version is built on an earlier version of the engine and has way more jank.
There are a lot of 'automatic' sections that fail for seemingly no reason. And inputs sometimes just do random things because it does have the problem of, in trying to make a simplistic control scheme, having certain buttons do too many things that if it does the wrong one, you die horribly, notably switching rails and jumping off rails. Personally I found the best way to make sure I mostly did what I wanted to do, was to make sure that the stuff I wanted to do, I took a quick breathe before doing anything, too many inputs too quickly really makes this game upset. Want to switch rails? well make sure I took a breathe after switching a rail, or doing the hoppy acceleration thing.
The second thing that it took me a while to realize is how super super important the attack upgrade things are, it changes the damage and the visuals and even mechanics of some of the moves. You get one by going through checkpoint with a character, or in certain balloons/item boxes etc. . . and each c haracter can hold 3 (it shows them on the thing) it turns tails air attack from absolute garbage to perfectly good.
a lot of the 'dashing off or hopping off cliffs' is something that's plagued 3d sonic for a bit, some of it is acceleration and just the game not always handling speed well. Given how big an improvement sonic heroes is over adventure in the sense of feeling in control of the character it's a good step forward, but it is something that for the most part gets better, like generations had much better 3d controls and platforming.
Depth perception/the camera are big enemies, or were to me too, and again I think that's some just due to nature of 3d platformers at the time, and good cameras being hard at the best of times, it's an art where it feels the divides keep getting bigger, but it's hard to really appreciate a great camera because it feels that's how it should be, and very very easy to recognize a bad or shakey camera.
In the end I always felt like this was one of my favorite 3d sonic games, I loved the aesthetics, theming, and personality of the game and it's like, if they spent a year or two refining or rethinking some of the ideas, it could be one of the best 3d sonic games very easily. personally I remembered thinking the 3 teams should have been the switching, like a speed team, a flying team, and a fighter team and having the mechanics and exploration be drastically different, but then there is this issue that it'd be hard to get people to really want to play something other than speed team.
in the end, it's flawed, and in some ways massively, but when there's good, there's so much good.
And also, Ross, I have no idea why you had an aversion to checkpoints. Did they say something mean to you as a child? Did you just hate that they almost always came with a dialogue line? I think you really need to s it down with your therapist to hash out this clearly deep seated issue.