We drove the 17-mile road up and through the canyon itself, and then into Kokee State Park. There are many, many dozens of lookout points to stop at along the way, and try to stop at them all--not just the "official" very touristy ones. Take Waimea Canyon Drive, NOT Kokee Road, as the latter is filled with slow tour buses and is not nearly as scenic.
We stopped off at the entrance to the Black Pipe Trail and took about a 5-mile round-trip hike to another lookout point. Honestly, what we saw was not that much more spectacular than all the other scenery we'd already seen until then! But it was a nice, easygoing hike--a bit steep at times, but never very difficult or at all dangerous. Definitely worth the trip!