We just returned from nine nights on the Big Island, and it fits the bill. Kauai was tempting to us, too, but the snorkeling there can be a bit iffier, and that was important to me. I'm so glad we were able to snorkel as much as we did. It was the highlight of the trip for me.

The Big Island IS big, and you sort of have to accept that you will not see/do everything you'd like. It's a really cool place. We spent our last morning sitting on a beach. Otherwise, we were in motion.