I upgraded to Wordpress 2.5 this evening. I am not really sure why I went to the trouble of doing this, since I am now a contributor to the Habari project, and would like to get my blog on that new platform soon. However, I wanted to see what all the fuss was with the new admin interface for Wordpress. I guess I am not as offended by the blue tones of the admin as other designers seem to be. In fact, I find it quite soothing. Still, I don't like that category selection is now "below the fold". And the tagging interface seems to be begging for tag clutter, since it doesn't list any previously used tags.
The reason I did not immediately jump to Habari is that I am still rather fond of K2's advanced search and navigation features, and these have not made their way to Habari yet. Ironically, these features now seem to be broken after upgrading to WP 2.5. This may mean that I am going to change over to Habari sooner rather than later.
UPDATE: I got the search and nav features to work again by following the suggestion in this thread.
I was not aware that some users are unhappy with the new admin interface. I think its fantastic. I'm still getting used to the tagging, but overall i think that 2.5 is a huge improvement.
I agree that it is an improvement. However, they still need to think more about their menu system. I have used Wordpress for a long time, and it is still not intuitively obvious where I go to do certain functions in the admin.
If you want to see some commentary from the unhappy folks, check out this post and comment thread. When you are done with that (and if you have a lot more time to spare), you can see these two video blogs from the creator of the kubrick theme which ships with WP.