I recently had a chance to take a look at the Alpha 3 release of Ubuntu 11.04, the latest version of Canonical's Linux desktop OS that is due in April. 11.04 is considered to be a major release for Ubuntu because it represents a significant departure from the default GNOME UI to the new Unity UI.
(EDIT: In the video, I state that Unity is written in the Qt Application framework. In actuality, the 3D version that most users will see is written in C++. Only the 2D version uses Qt.)
Unity doesn't so as much replace GNOME interface entirely but acts as a replacement shell layer for the default GNOME 2.3.x shell.
Unity has received quite a bit of criticism from the GNOME purists because it was developed entirely in-house by Canonical without consultation from the greater GNOME/Ubuntu and Open Source community at large. Much like Steve Jobs drives many of the design changes for Mac OS X and other products at Apple, for better or for worse Canonical's Mark Shuttleworth decided that the future of Ubuntu's desktop was going to be with Unity.
First, the good stuff about Unity -- with the 3D alpha-blended effects it looks very pretty and overall it tries to make the OS friendlier for the average end-user. Linux distributions and Ubuntu specifically has often been criticized for lagging behind both Mac OS and Microsoft Windows in terms of desktop beautification and user-friendliness, so this is a step in the right direction.
For the Linux neophyte, Unity is good news because it essentially reduces the menu complexity of the GNOME desktop into a vertical "Launcher" which displays running tasks and favorite applications/programs. It also integrates a search engine that helps users find their way around the system.
However, as you can see in the embedded video and in the accompanying screen shot gallery, the way the desktop behaves is very different than previous versions of Ubuntu and on other GNOME 2.3.x-based Linux distributions.
Unity has chosen a very Mac-like approach by where the foreground application menus are displayed at the top of the screen where the main GNOME menu system/Nautilus navigator used to be (although this legacy "Places" menu appears along with the file management dialogs if Nautilus is actually running).
This takes quite a bit of getting used to.
Additionally, the Unity "Launcher" that functions as an icon bar and task manager which is on the left-hand side of the screen is not yet easily customizable. There's no apparent way to move it to the bottom of the screen (so it more resembles Windows 7) or to the right of the screen a la old-school NeXTStep, the forerunner to Mac OS X where the paradigm originated.
Additionally, you can't right-click on the bar to add widgets like the old GNOME panel, and you can't add favorite programs to it unless you search for the program in the search engine (which pops up if you hit the Windows/Super key), and then drop it into the Launcher.
There's also no default icon for the Control Center and many of the other typical Ubuntu common tweaking and configuration applets that you would normally find in the legacy GNOME menu, although they can be easily added and found via the integrated search engine.
Unity is still very much a work in progress in terms of it being able to completely replace all of the functionality of the traditional GNOME menu system and traditional UI.
Fortunately, for power users, you can still return to the old GNOME 2.3.x UI by choosing "Ubuntu Classic Desktop" during the login process. For those of us that are not quite ready to migrate to Unity yet as our default interface, that should be welcome news.
I'm not sure entirely what to think of the changes as a long-time Ubuntu user. Clearly, Canonical and Ubuntu needed to do something drastic in order to differentiate itself from Debian, Fedora and OpenSUSE and to advance the Linux desktop to a more modern, user-friendlier system for the average person.
Hopefully, it did not do this at the cost of alienating much of its core user base, and they'll listen to user feedback as Unity is used by more and more people in the coming months and years.
What is your impression of Ubuntu 11.04 and the new Unity interface? Talk Back and Let Me Know.