This is amazing and not to be missed. Watching the little penguins get up the courage to charge up the beach--or wimp out and run back in the water--was a lot of fun. Hearing the noise they made in the bush as they reunited with their mates was also incredible.
We paid the extra to get a ranger-led tour and were very happy we did. We got prime seating to watch the penguins come in out of the surf, and then got to see a few places that general admission won't get you. The ranger also provided loaner binoculars, and radio headsets so we could hear what she was saying at all times.
Be advised that photography of any kind is not permitted--not even if you disable your flash. Too many people either thought they had disabled their flashes but did not, or simply flaunted the rules, and the park service decided that the blinding effects on the penguins were not acceptable.
Also, you should dress warmly. It got chilly the evening we were there.