I have been leading a good sized Angular app for work for the past 8 months, and upgrading from v2 to v4 has been painless, even while having an AOT compilation build pipeline set up - the only modifications we had to do was switch OpaqueToken to InjectorToken, <template> to <ng-template>, and Renderer usage to Renderer2, and these weren't required to be done yet. We only did those changes to get ahead of the curve from the deprecation messages.

On first note, the codegen size decreased dramatically for AOT compiled builds - we went from ~600 KB vendor + app minified and gzipped (not counting 50 KB of polyfills) to ~400 KB. This is huge, and the boot speed feels even faster on first user load of the page!

Thanks to the Angular team for this fantastic work!