My experience from about 5 years ago was that the routes are mostly quite short but on fantastic quality rock and have really cool moves, although the grades can leave your ego feeling a bit battered!
Good move. Of all the European guidebooks I've read, Markus Schwaiger's comes closest in spirit to a good British climbing guidebook. He's trying to convey some of his love for the area, the history and the climbing characters (there are Zillertal locals who were trying trad 8a ground-up in the Dolomites in the 80s) and not just provide a climb-by-numbers topo.
Good to hear Zillertal is a beautiful place and has some great climbing, i'm heading there in 10 days time for a few days. Just keeping fingers crossed for decent climbing weather now!
It's a fantastic area for climbing and a beautiful place to visit. There are routes of all sizes and world class bouldering. Didn't seem that stiff either in my experience?
Have fun, the guide is really good and has everything that you need in it.