IV's great, but Rondo is also. What's wrong with both rocking?
I like that Rondo doesn't have multi-directional whipping. It doesn't need it; it's designed not to. It's like an upgraded Castlevania I and III. It even does the alternate paths thing better than III, in my opinion. It has a very unique way of reaching alternate levels and I love how most stages have lots of secrets and different ways of reaching the end. It's an adventure game mixed with the classic linear design of the old games. It kind of is an exploration game, and is what I'd like to see fleshed out in a future title: taking the classic platforming Castlevania gameplay and combining it with the exploratory, open-ended nature of the SOTN-style games (though more restricted than those games; it would obviously be designed much differently, and there wouldn't be leveling up and all that).
Rondo is a perfect game. So is IV. They're great in their own ways.