Unity has seen improvements - especially the inclusion of a fallback 2D variant is an important addition to the still relatively new desktop shell. Several aspects have been visually refreshed, and the Software Center, too, has been overhauled for its version 5.0 release. It's got a new interface, which includes, among other things, more ways to bring specific applications to prominence - something application developers selling stuff in the Software Center will surely enjoy.
Sadly, all this comes at a price: GNOME 2.x, which was the fallback classic desktop option in the previous release, has been removed from the default install image. Of course, it's a simple
apt-get install away, but now it's not just a second class citizen - it's a third class citizen. GNOME 2 is slowly but surely dying, and with both GNOME 3 and Unity not being to my liking, I've decided to make the jump to KDE 4 (any distribution suggestions? Debian-based please!). Xfce was also in the running, but for some reason, it didn't fit me very well.
As far as email clients go, Evolution has been replaced by Mozilla's Thunderbird. The GNOME Display Manager, gdm, has been replaced by LightDM, which has also been themed to fit into the Unity look and feel. In yet another brain-dead annoying decision, Synaptic has been removed from the default installation as well. Ubuntu One will be shoved into our faces even more, so that's another something to look forward to. In the meantime, Canconical maintains that Ubuntu is still something expert users can enjoy.
"Ease of use, stylishness and key tasks such as safe web surfing, document sharing, office productivity and personal clouds for music, files and photos are central to the Ubuntu experience," Jane Silber, CEO of Canonical, said, "That's why Ubuntu is now a global phenomenon - not just for system administrators, developers and expert users, but for a growing community of home users that want a simpler, safer way to use the PC."
You know the drill here - the update manager will perform the upgrade to the new release. For new installations, go grab it from the download page.