I visited 3 caves at Waitomo - the Ruakuri cave which has a 1.6km long tour path and a spiral man-made entrance, the Aranui cave which was much shorter but more impressive inside, and the Waitomo Glowworm Cave. Most of the cave photos here are from the Aranui cave.

This is the 3rd cave trip I've done, while Jenolan in Australia was more impressive in terms of the formations, the rooms here felt bigger.

As for the glowworms in the glowworm cave, they're plentiful and much more concentrated than in the glowworm cave in Te Anau (on South Island). Also impressive was when the guide shined a light on a large cluster near the walkway illuminating their strands of silk. You're not allowed to take pictures of the glowworms (imagine 50 people at once with their flashes trying to photograph tiny specks of light), but the cave's website has some great photos showing the strands: http://www.waitomo.com/Glowworm-Caves/Pages/Waitomo-Glowworm-Caves-Photo-Gallery.aspx

In addition to the tour caves, there was a nice trail to the Ruakuri Natural Tunnel - a cave where most of it has collapsed leaving just a short tunnel portion.