Let's ignore the fact Shiseido reformulated their original Zen countless of times, released different perfumes in various bottles (white and pink) under the same name and took it in and out of the market in some countries more time than I can track. I hear the current juice sold in the black bottle (apparently Nordstrom has it) is nothing like the 1964 version, so I haven't bothered with it as I have a couple of old eau de cologne bottles and they're very lovely.
A quiet woody floral is rarely my thing, especially poorly made modern ones (thinking of Lancome Magnifique), but Shiseido managed to bottle a delicate quality of a sheer rose over an even more sheer incense. The opening is a little aldehydic and has an abstract white floral veil. A bit later Zen takes on the zenish character that makes it for me a perfect nap time perfume- the wood is soft and smooth and the incense is subtle and barely there. I like both elements but somehow it's the rose that wins me in this case. It feels white or pale yellow, not the more common jammy red ones. It doesn't turn sour or takes over the room. I would actually say it's a rose many men would find wearable.
The sillage of Shiseido Zen (at least in the version I have) is almost non existent. It can only be smelled within one's personal space. I used to feel it didn't last long and would reapply after a couple of hours, but eventually I realized that there's some type of musk there I can't smell unless I'm paying close attention. Once the rest of the wood takes over Zen is fully back and actually lingers nicely on my clothes (and blankets, considering I really like the calming effect).
I have no idea why Shiseido found it necessary to mess with this classic, but thankfully older bottles can still be found at vintage stores and yard sales. I wouldn't buy it on eBay because I have no idea how to verify the date of the bottles, so be careful if you are on the hunt for old juice.