Suzhou part of trip disappointing. Long drive to see one garden - and not the most famous one - and silk factory. Not worth it. Zhouzhuang part of trip excellent. Would just do this part next time and go to Suzhou by myself.
In my view this is not worth it in as much as you simply get to the end station and then still require a taxi. However, it's a once in a lifetime experience to sit on the fast train.