The update from AngularJS to Angular 2 was a huge step forward, but it was also infamous for not being backwards compatible. In contrast, Angular 4 brought us new features while being backwards compatible. And now, six month later, the latest major release is available.
The upgrade to Angular 5 is an incremental one. This is because many of the changes are done invisibly.
However, some breaking changes have been included, so some developers will still have a lot of work to do. But for all the developers who kept their code bases up-to-date, the changes will be easy to handle this time.
The focus of Angular 5 was to make Angular faster again. The loading time has been improved by smaller bundles. The execution has been improved as well by optimizations at the compiler. For some projects, it is also important to note that the ng-upgrade is still in progress.
This allows AngularJS applications to be migrated smoothly to Angular and vice versa as Angular components can be embedded as downgrades in AngularJS applications.
Additionally, experimental technologies and features can be developed in a special lab space outside the Angular Framework. They can be evaluated and tested by developers at an early stage without negatively affecting the release planning of the framework itself.