I recently watched a nice show on the national parks of Hawaii; the Hawai'i Volcanoes National Park has a lot of appeal to me in no small part due to our experience here. The results are much further removed from the eruption here, but in some ways more spectacular for it. It's easy to see the results of the eruption, but there are also fascinating plants throughout the park as well.
This park was on our "possibly visit" list, which we mostly ignored because of how many things were on the "must visit" list. This was the first time we explicitly visited a park because of our experiences with other national parks.