GNOME 3.14 is releasing in September and Ubuntu-GNOME in October, therefore this is an early access to the development versions of both of them. However Ubuntu development releases are quite stable and the same also applies for GNOME, so it should be a very usable system.
Running GNOME in Ubuntu won’t give a genuine GNOME experience and not all things work as supposed to, but on the other hand Ubuntu will give you the best out of Linux desktop (the term is wrong) in general, meaning easy access to all available software, free and no-free.