There are a lot of easy green trails and pretty smooth flowy trails that are fun. For easy smooth, The Dipper is probably a little too pootle but test yourself out whether you can hold on, but nearby are the "Challenge" tracks which are fast, flowy and pumpy but not rattle fests. A few other tracks down the bottom that are beginner but still fun. After this stuff like Dragonstail and Mad If You Don't are just fun even if not techy.
One thing to remember about Rotorua is that there is essentially no rock. You have roots,lots of brake bumps and droppy features, but some tracks are pretty much smooth. So you may find some places to ride even on the shuttle tracks?
Lots of other things to do in Rotorua, visit the vistor center for millions of brochures.
My daughter loved the Zipline
http://canopytours.co.nz/
But go to this bakery every day and get fat, almost as good as the riding... Ciabatta Bakery
http://www.ciabattabakery.co.nz/