I don't really care to rank the areas in RE4. Typically, I would tie the castle and the Island, and put the Village slightly behind both, but really, that's not necessary. What was brilliant about RE4 was that, despite its length, it never really dragged that much. Every time you were led into a new area, some new scenario was thrown on top of you. Yeah, a lot of the times it was just fending off a bunch of enemies, but the environments were varied enough to keep it fresh.
For a game that's 15-30 hours on the first playthrough, it had amazing pacing. I always view the village, castle, and island areas in their own distinct way, because each of those areas introduce new environments and gameplay scenarios for the player.
I can see why some might see the castle segment as dragging, but really, the castle isn't even all of the castle segment. The caves, the mines, any underground areas and outside areas, all make up more of the castle segment than the actual castle itself. That said, 1/2 of the game happens in between the village and the island, so obviously the castle itself is labeled as one overlong chunk, even though every area inside of it is quite varied and interesting; everything from sniping catapult guys, to fending off creepy creatures in the sewers, to exploring a garden maze with dogs jumping out at you, to riding on a mine cart while fighting villagers, to running away from a giant Salazar statue.
And I just have a love for the castle interior in general. It gets me every time. Areas like the one where you have to place the King's and Queen's grails are just really cool to me, how you're walking along and all you can hear is the wind in the background. Awesome. Just like the corridors on the island, these areas remind me of good ol' claustrophobic RE.