Let me begin with the same disclaimer the Joomla team stars with - this is an ALPHA release and a lot of the functionality may be broken or not there. Indeed, ACL is not in the first release and everyone knew that going in. They aren't kidding, it's still pretty rough, but it's still a look at what is coming.
I got my copy and did a pretty standard install. This is one thing that Joomla has down pat. The install was flawless and I had a functioning site in the time it took to upload the zip file and unzip it. Since I am a glutton for punishment I installed with no sample data - big mistake, I think I am going to reinstall with the sample data so I can see how some stuff works.
The first thing I noticed was that the Content menu item is gone. It has been renames and relocated to a more appropriate location, Articles in the Components menu. Since the content was really just a component it's fitting that it's listed there now. The Section manager and Front Page managers are also gone. We are left with the Article manager, the Category manager, and the Featured articles manager. This is much cleaner and easier to understand for a new user. As expected, the categories can now be nested as you see fit, but I was not particularly excited about this since I have been testing various CCK components.
The article editor has seen some pretty big changes as well. The read more button is still there (not for long I would imagine) but we are back to an intro text editor and a full text editor. Again, this seems to make more sense for a new user and a little more intuitive than the read more line from 1.5. This is where I noticed some new buttons - Save As Copy and Save & New. Both very handy for sites that do a lot of updates.
Last thing I want to mention in this quick look at the new Joomla is a feature that I am really excited about that hadn't really been publisized in the feature listings. A lot of the new features can already be achieved with extensions, with the exception of the new menu assignment options for modules. It doesn't appear to be working properly, but there are two significant changes. First, within the module menu assignment there is a new option to deselct a menu. Previously we were limited to All, None, or Selected. While All and None worked well, Selected had an inherent problem in that it excluded future menu items and you'd end up with holes in your site any time you'd make a new menu. Presumably the Deselect from list will allow you to exclude certain menu items, thereby including future items.
Second, module assignment can also be controled at the menu level. Basically, you can pick and choose module assignments right when you make the menu to begin with. This not only makes it easier and more convenient for the admin, it also makes the system more powerful with more finite control over what appears and when it appears.
Overall, Joomla 1.6 looks very promising. I know there is some work to be done, but this release is making some big steps in the right direction.