Enlightenment has been quite interesting to me. It has not even got a beta release so far yet I like to use it. That is because, it does things differently. It is very efficient, keeps the CPU far more cooler than any other desktop environment, has nice effects already built-in, and is far snappier than most mainstream desktop environments [I am not interested in comparisions here; so I won't point to any other desktop environment in particular.].
However, there still are some issues [Actually, when you install E17 and read the about dialog, they clearly acknowledge that it is under "heavy development"].