I got directed here from a YouTube video go someone doing a custom level (Nitro Fun). Very impressive! The levels definitely capture the feeling of Crash gameplay, and it was nostalgic to puzzle out how to jump on series of boxes over bottomless pits once again. I also like the Mario style of rewarding skilled gameplay with harder bonus levels.
Unfortunately, the engine gives me a similar uncanny feeling as Pokemon Essentials -- it's so close to the real Crash style that the few differences (some of the movement physics and the dynamic camera, nitro crates not jiggling, etc.) become all the more jarring. I don't know if you plan to touch that up for v1.0, but the closer you can get to emulating PS1 Crash the better. (The dynamic camera is a particular issue, as this YouTube video explains.)
I also encountered some bugs in Castle Mania: Only some of the wooden platforms fully retract (for the ones that don't, you can walk on the sliver even when fully retracted); the moving wooden platforms create some momentum glitches where Crash continues moving in the direction of the platform when he jumps off it; and it's possible to climb on the slidey-stairs even when they're retracted. I also didn't realize the autosave didn't produce a hard save if you quit to main menu, which was a nasty surprise.