I'd like to talk about Portrait of Ruin. What a masterpiece. It's such a shame that people fail to see how brilliant it is. Okay, it had a bad story and bad character art and overall the atmosphere is kinda lacking when compared to the rest of the franchise; I don't mean to claim that it's perfect in every way, it has many flaws.
But gameplay-wise, it is the absolute best. It is incredibly smooth, the weapons all have a perfect feel and are super varied, and having the two characters allows a kind of flow that's not been matched by any other Metroidvania that I know of. It is simultaneously rigid and precise on one hand, and super dynamic on the other, like playing two instances of Dark Souls at the same time if you see what I mean. I think the devs tried to replicate this with OoE's dual-wielding, but obviously it wasn't as successful, even though the resulting system is kinda interesting. The gameplay, the level and monster design, the mechanics of Portrait of Ruin stand head and shoulders above that of any other Castlevania.