Adapta is a shiny new material design like GTK theme. It supports numerous desktop environments including Gnome, Budgie, Unity and Cinnamon.
You may already test the – yet unstable – next version of elementary OS. Loki can be installed on top of Ubuntu 16.04 using a PPA.
Check out elementary OS 0.4 Loki running on top of Ubuntu 16.04 beta in a 2 minute video.
GNOME 3.20 now support OS upgrades, has many updated core applications including Files, Photos, Calendar, Builder, Maps, Polari and more.
A slightly modified version of the beautiful Arc GTK theme has been released with OS X styled window buttons.
A long awaited feature just landed in Ubuntu 16.04 LTS: Unity launcher can now be moved to the bottom.