I have been there once, on halloween day last year and I have to say that I didnt't really enjoy it. While getting there by public transport from Munich City Center was ok (even though it takes an hour and requires walking about half a mile, and you can take a bus to/from MUC which will take about half an hour with one change at Erding station), the entire experience didnt't quite live up to the image portrayed in the media. As it was a monday before a public holiday, the entire thing was extremely crowded (not every guest would receive an own locker, but you'd have to share a single locker with your group), both in the general area and in the sauna area, which didn't really make the experience too great (you usually wouldn't catch a seat in a sauna where an "Aufguss" would take place unless you'd arrive half an hour in advance), and the entire building is quite confusing and not really well signposted (particularly the sauna area) - in my TripAdvisor resumé (3 out of 5), I suggested that I'll probably not be coming back.
However, wait times at the water slides weren't too bad, hardly any wait for more than 10 mins, however, I'd say that particulary the water slides aren't half as spectacular as I would have expected them to be.