Being able to easily hop on/off the Shinkansen has by far been one of the highlights of my life. An absolutely incredible experience and the JR Pass gives you the ability to do that. However, I would only recommend if you'll be visiting a lot of cities; otherwise you won't get your money back (e.g. if you just use it to get around locally in Tokyo.)
However it gives you inspiration on destinations you may not have previously planned I your trip. For example, I went to Miyajima Island (Itsukushima) off the coast of Hiroshima and only because I realised I could get there completely free - the pass even covered the ferry!
It be and my most favourite place on earth.
All I have to say for the JR Pass is a huge thank you - it really made my Japan trip.