App Explorer is no longer shown by default. However, I find it to be the better view than Project Explorer:
- you're far less likely to launch the wrong project using App Explorer than Project Explorer
- The view is simpler, because you don't see a ton of unrelated files/projects (which is important for developers with many projects)
- App Explorer includes a "search-whole-project" text field, which is handy
My preference is to have App Explorer returned to being the default file tree view. In lieu of that, having it conveniently accessible on the Window > Show View menu will suffice.