The only two things in this game that good are graphics and music (to a certain extent). Gameplay is awful. Slowdown non-stop and collision issues. And all this is in the game which almost on 70% consist from platforming!! Which means making accurate jumps is very important thing, but it is hard to do because you can't calculate your speed due to the slowdown, little to no animation and sometimes wacky collisions. I said it already - it's as if game engine and actual level design were created separately from each other. It's really strange issue, but this game is just plain bad.
You can get used to it and even enjoy this game to some extent, but what for, when there are many other games in the series that did everything right?
P.S.
It is should be called "Castlevania: The Slowdown".