It seems to strike just the right balance between being a modern game and yet still retaining the feel of the original games for nostalgia.
Importantly, it's based mostly on the third in the series, when the character could change into various animals. That was when it took on a kind of Castlevania feel, in that there were areas you couldn't access at first, but which opened up later. The typical examples being when you can see a ledge early on but it's too high, and when water is blocking your path - but later on, you gain a double-jump ability and the ability to swim. (Not that these are necessarily in this game - I'm using generic examples to avoid spoiling).
To me, that kind of thing is what really makes games fun. It creates a sense of exploration and makes you feel clever when you remember to return to a certain place after unlocking a relevant skill.
Unfortunately, there's one, tiny bit impactful problem. The character moves *so* slowly for a modern game. And to compound the issue, much of what you do involves both back-tracking to previously travelled areas (to try out new abilities), and falling off things only to have to go back to the beginning where the only ladder is, etc. So the character speed quickly becomes a frustrating, dragging experience.
It looks like you might be able to unlock 'shoes' with greater speed values. But making the early game dull in order to build to something better later on seems like a pretty poor design decision.
Still, overall a very solid continuation of what was one of the greatest series of games of its time.