BackTrack is really nothing special from a UI standpoint, however these screenshots only touch on it's capabilities.
BackTrack is meant to be used for network penetration testing, or in other words ethical hacking into corporate intranets and other networks in an effort to cover up security holes so unethical hacking cannot be done the same way.

Like I said, I only touched on it, and if you want to really see what it can do, then you can download BackTrack from here.

The default desktop isn't special. Note that, however, by default (at least with the pre-configured VM image) the X Windowing System doesn't start up automatically and must be launched by typing startx at the command line.
All it is, is Plain Jane GNOME 2.30.2, in fact BT5R3 (what I'm running) is based on Debian.

There are hundreds, if not thousands, of penetration/stability testing tools bundled by default, in fact I think 80% of the space BT takes up is used by these tools alone.
Since BT is meant for penetration testing, there isn't an abundance of other applications installed; just the basic stuff that would be necessary (a file manager, web browser, and a few other things).

This is Terminator, which is a group-based terminal emulator. You can run groups of terminal windows together, and each window can be designed to interact with one another or group to group.

This makes managing CLI tasks alot easier.