How do you break from a past and become your own artist? By coming to terms with what you used to sound like and then cleanly moving on.
Robert Plant attempted to branch out with Pictures At Eleven from his Led Zeppelin past and couldn't quite pull it off, while The Principle of Moments was a step in a new direction. Now and Zen 
embraces the Zeppelin past (witness the four symbols on the cover and the appearance of Jimmy Page on one track) but also forces the listener to take Plant on his own terms and go with him on the way forward. It's kind of like a one-off reunion show for closure.
The songwriting is first-rate, melding rock riffs with keyboards and a bit of new wave sensibility. "Heaven Knows" is an efficient pop single with muscle; once that is out of the way, Plant gets down to business. "Tall Cool One" is where Page comes in, laying down riffs between the words ("Lighten up, baby, I'm in love with you") before Plant growls the inane chorus. The song closes with a pastiche of samples of various Zeppelin songs, for no reason, almost like a big middle finger to fans who kept clamoring for a Zep reunion rather than hearing what Plant had to offer as his own man.
"Ship of Fools" is a beautiful song, with Plant restraining himself to his lowest register to turn in a minor classic. "Billy's Revenge," "Helen of Troy" and "Why" are all solid rock songs, unique to Plant and bearing the stamps of 80s production (cavernous echo on the drums, etc.). "White, Clean & Neat" is nothing like Plant had ever done before; only his voice, spare percussion and the occasional guitar riff carry the song.
A few midtempo tracks clutter the album, such as "Dance On My Own" and "Walking Toward Paradise," while "The Way I Feel" could have been great but is just lacking something.
By enlisting a keyboard player and embracing his past, as well as writing some of his more direct lyrics, Plant created his finest solo effort to date. For those wanting to dig into the man's solo catalog, especially Zeppelin fans who have wondered where to begin, this is a great place and a solid, if not great, album.