I recently completed the excellent Oracle video tutorial on Oracle JET and created a simple Linux dashboard for a server using JET. Basically, I really enjoyed learning and using JET and found building a web application using JET very easy. The Oracle JET Cookbook is really excellent, for sure.
Of course, with all things in the universe, there are good and bad, plusses and minuses. So here is my review:
A Quick Web Developers Review of Oracle JET
I encourage all web developers to try Oracle JET and see how JET fits into your web dev projects.