Boy, nothing says "This upgrade is a totally backward compatible drop-in replacement for Angular 2" like not only bumping a major version number but actually skipping over the usual increment entirely.
(Not that this is really substantial -- it's the history of the project that not only warrants but demands skepticism on the ease of both the upgrade and the utility and learning curve. The tone-deaf nature of the upgrade number is simply frosting on the cake.)
I agree that skepticism is important, but this is honestly really straightforward if you've been following the development and community discussion. IMO the Angular team made it rather clear why they were skipping the 3rd increment (router package was on 3 and they wanted all of the packages to be at the same increment) and that upgrading version numbers was just semantic versioning and not releasing of a new framework like Angular 1 to 2 was. There were also a few popular articles explaining that no one should be freaking out over the 2 to 4 change and a lot of discussion on HN.
So at this point, a few months into Angular 4, it's simply wrong to make the comment that the OP made.
It's true, the nature of the changes from angular 2 to angular 4 are actually smaller and easier to deal with than some of the changes between beta release candidates. But now we're poised to be able to actually build some applications without so much infrastructure change.
(Not that this is really substantial -- it's the history of the project that not only warrants but demands skepticism on the ease of both the upgrade and the utility and learning curve. The tone-deaf nature of the upgrade number is simply frosting on the cake.)