There was a glitch or something that wouldn't let me change the difficulty from Easy to anything harder or even Casual, which was easier. If someone can tell me why this happens I'll make a note of it for future players, but it was frustrating to not play at the level I wanted to.
I think the game is still good, however, and if you like classic Sonic games you'll like this one.

StEJ2's Challenge Mode is a game mode that insists upon its difficulty, while still maintaining the hallmark jankiness of the franchise, which usually ends up trivialising boss fights. They still end up being the only engaging parts of the experience, especially in the late-game where stages just have long stretches of precision platforming segments with few checkpoints in between. If you're able to wall-jump while using keyboard controls, I'd recommend foregoing playing with a Gamepad just to make your life easier.

i hope lake feperd sees this and is proud knowing that i tortured myself for a ♥♥♥♥♥♥♥ year trying to get the F.M city platinum time medal.