Having now played through the GBA trilogy of Castlevania games, I can say with utmost confidence that this one is my favorite. It's not my favorite Castlevania title overall, but it's a tossup between 2nd and 3rd place for me.
The gameplay in this game is absolutely great, the abilities all felt nice to really maneuver with. Having a large assortment of weapons was also really nice, and I really enjoyed experimenting with ones that seemed like they could be fun to try out. Navigating through the castle was fun, and like always it feels rewarding to find secrets, or check back on areas I've been before.
The Soul Set system is easily one of my favorite parts of the game, though at the same time it's rarely necessary outside of exploration. Even with the little use I got from it, I still like how ridiculously customizable it is, and how it can create so many unique options for me.
I found it personally a tad bit easy, but hey, just because a game is easy doesn't make it bad. One boss in particular did really annoy me though.
Regardless though, this is a great Castlevania title, and though it's not my favorite, if you're looking to get into Castlevania as a series, I'd probably suggest this game to be the starting off point.