The visitor's center is awesome, with tons of information about the park and lake. Many of the exhibits are interactive so the kids really enjoyed it as well.
When you get out to the crater it's difficult to see much due to the steam but that makes it even more dramatic. There is a higher peek you can climb for a different view but it was closed the day we were there.
Side note - the bee hives lining the trees on the way up are really dramatic!