This is super neat! That being said, this is a alpha proof of concept build, I do have some thoughts. As much as I liked the original game, I do feel this project's potential is being limited by the design parameters set by the original and how it feels.
Firstly, while the controls are definitely more responsive with just buttons than with motion inputs, I don't feel as in-control as I'd like, though I think this is partly because of the original game's design and animations. I feel like I'm fighting against Sonic's movement controls regularly, especially when jumping, and the sword swings don't feel quite as responsive as I'd expect from a combat-focused game (his sword swings feel sluggish at times). I think a bit part of it is the hyper on-rails design and the inability to move backwards at a speed faster than a snail's pace, on top of Sonic's acceleration being absolutely awful without using the forward jump.
Also, as neat as Galahad's boss fight is in concept, I can't help but realize it's a QTE-fest (same goes for King Arthur, too). It sorta made sense when the focus was on motion controls in the original, but here having to wait for the button prompt to appear to deflect or avoid an attack just isn't fun, and the approach segment isn't really challenging or mechanically interesting either (it's just a row of projectile spawners).
I think the main things that need changing would be making Sonic's sword swings much faster and more responsive and revamping the movement to be more free-form and not as tightly bound to the on-rails structure (aside from the sequences where it makes sense to force Sonic to be completely on-rails, but in general it would basically be linear corridors with invisible walls otherwise), or at least offer that movement type as an option. You're already adding new content and mechanics to the game, you're not obligated to limit yourself entirely to the original's mechanical design. Free-form movement would also provide more opportunity to revamp the boss designs. Imagine if the game feel took cues from Strider or Metal Gear Rising, it would feel amazing to play.