Aight, just beat this with both characters. Contains alluding to spoilers so be warned!
Axel? Ehh, I like the movement but I'm not sure it works with platforming and combat that demands a lot of pin-pointing. I feel like his fighting against bosses and enemies is awkward and easily abusable with i-frames at the same time. Cute character tho. I'm not into classic Sonic much so take what I say here with a grain of salt.
Meanwhile, I really enjoy the general gamefeel with Hazel. There's a certain kind of flow to it. I've strongly considered picking up speedrunning this game, but there's an elephant in the room...
The final platforming level.
I'm someone who can enjoy hard levels but a lot of it feels plain unfair with the sheer amount of off-screen death traps, blind jumping and (also off screen!) enemies placed right below warp spawns.
There's an oversight near the start of it where if you come from the top, there's a straight up dead-end and the ladybugs won't spawn if you fall from there. It's a wide open space so...uhh good luck getting back to the left as Hazel with no enemies remaining.
In worst cases, the off-screen death traps can ruin the flow. Take the wall of death for example right after you fall through the floor warp. You can't see it in time and have to come to a screeching halt once you know it's there. It's designed against the normally high-speed, flowing gameplay.
There seriously needs to be a checkpoint right before the difficult platforming section, or at least made easier. As a seasoned 2D platformer player who got irritated and burnt out having to redo relatively easy platforming over and over, I dread to think how casual players will cope at all.
While I have bunches of unmentioned nitpicks, I'll settle with this for now. I know I sound critical, but really care about the game.
EDIT: Oh yeah, does anyone find the game frequently minimising, especially after dying? I never get this with other windowed games and they aren't forced to be on top. Something is up.