Meh... Waiparous has its spots that can be a little tricky... just depends where and WHEN you go.
My last trip out there was after about 2 weeks of heavy rain. I didnt realize just how brutal a couple sections of the trail were going to be. It actually made 1 bypass completely impossible and i was "forced" into a tank trap type hole. Thankfully... i was able to drive out of it... but it could certainly have been worse.
If you stick to the main trail out there, Waiparous Valley Road straight out to the falls, its not bad by any means. There are a couple spots that can get tricky depending on the time of year... but its generally a simple run.