I recently traveled by 2-night ferry from Shanghai to Kobe, and then back to Shanghai from Osaka on another 2-night ferry. I put my comments in the flickr albums, under the album title so as not to clog up this site.

Shanghai-Kobe on the ferry "Xin Jian Zhen"
booking info and sailing schedules on their website:
http://www.shinganjin.com/index_e.php

My photos and commentary (click under the album title for the full journal): https://www.flickr.com/photos/141333...7645464516132/
More photos: https://www.flickr.com/photos/141333...7645461236161/
Osaka-Shanghai on "Su Zhou Hao"
Sailing schedule and booking information on their website: https://www.shanghai-ferry.co.jp/english/index.html
My photos and commentary: https://www.flickr.com/photos/141333...7645490333231/

Overall it's a great way to travel between Shanghai and Japan. I recommend it, though on Suzhouhao rather than on Xinjianzhen.