I'm a BIG fan of classic-style Castlevania, and though the controls in here took a little getting used to, it was all fine once I got the hang of them, I'm very glad to be able to find someone else with an appreciation for the old-school Castlevania experience! I'd still remove the delay from the Jumping though, Classicvania had a delayed whip, but not a delayed jump, and well, I'd prefer to use up + attack rather than just up to throw the sub-weapon, but that's just me... Also spectacular pixel art! Good job on that!
All that said though, I'm afraid this game falls a little too out-of-spec with the original Game Boy... Sure, you stuck to the 4 colours, the 8 x 8 pixel grid, the resolution, and even the single BG layer limitation, but you're not only rotating sprites (which the GB couldn't do) the music doesn't even sound like Game Boy music! It sounds closer to like, GBA music, except higher quality...