The most magnificent sight was an early morning - snow covered Ngauruhoe volcanoe on pink sky. I will never forget it.
In general - incredible mix of fierce wilderness, unusual beauty and hospitality of local people. If you are lucky enough to visit the site - try at least the track named Tongariro Crossing (consult tourism bureau before - often weather up there is too dangerous). It takes rather weary day, but it is incredible to walk so quickly from forests through tussock above snow line and back.