I've been looking around the newly available Windows Vista build, 5270, some this morning. It's starting to come together clearly, but I'm concerned about the lack of style of the operating system. Because I run in VMware, I cannot enable the glass effect so some of the UI flashiness is not there. However, there's more to an operating system than special effects.
I understand Microsoft has a lot of users to keep happy, and I'm one of many hundreds of millions of users, so my opinion may be in the minority.
What the current build lacks is style. What shocks me the most is that for the past 2-3 years, Microsoft Longhorn and Vista evangelists have talked about the styling of the system and how important that would be, not only to Microsoft, but to third party ISVs. Finally, the operating system could really be styled by graphic designers in the way they wanted using tools built for designers, not developers. No more hand-offs of bitmaps to developers who would do their best to emulate what the bitmap and functional or graphical specification asked for.
I'm sure Microsoft developers and designers are working feverishly to come up with a long lasting pleasent user interface. Right now though, all I have to go on is the recent December CTP build of Vista (5270).

Here's what looks like the new start menu for example. Except for Apple's OS X, it is nearly universal that the "Start Menu" equivalent in most operating systems is located in the lower left corner of the main screen. Most Linux distributions have copied it.
Maybe it looks better with a high end system and graphics card.
It's falling prey to a common style trend of reflective glossy buttons though that Apple started (or at least made popular). Why not try to innovate something new? Although I've seen no documented proof of this, I'd bet that Microsoft is working on other colorized versions of the menu. For now though - black makes me think "designer", not consumer or professional office user. OS X has a pleasent welcoming feeling, whereas this design is more brooding and depressing. I've seen that there supposedly is some way to configure the specific color (like black here) used in the system. However, it's only available on higher end video cards (found in Appearance and Personalization > Personalization > Change your color scheme):

More dark ...

As you can see, even more black when the Start button is clicked. (In the screen shot above, Vista is the machine name I believe). Nothing really too innovative about this new Start menu. I've clicked the "Power" button in the lower right corner expecting power options such as shutdown/stand-by/hibernate many times -- I bet I'm not the only one. Those options have moved:

They'd make more sense under the power button (with a similar style button).
On a positive note, I do like the non-cascading menu "All Programs" behavior now. For example. If I click on the "All Programs" option above Start Search, this is what is shown:

Clicking on "Accessories"...

Instead of menus and menus with pop-up menus ... it's in place. Actually, it behaves like a tree:

Clean. Simple.
One thing that hasn't changed in far too many years:

Still modeled exactly after a basic calculator, not taking advantage of any WinFX features or moderization that could be possible. It's not sizable, nor are the buttons labeled more clearly (M+? MS? MR? Why did they spell out Backspace fully though?). Maybe it will change. (Please!)
There are trends to make the system easier to use. The most obvious is the right click options on the desktop:

"Choose Desktop Background". Halleluiah! Finally a more obvious method for changing the desktop background! (I knew how to do it the other way of course, but it just wasn't obvious).
Here are just a few simple things that Microsoft should do:

Add some new pictures for assocating with an account! It's the little things like this that can make people smile and make the experience better.

In the date/time applet that shows up by clicking in the clock, it's great that I can look at the calendar without actually making changes to the actual system clock. Why not though make this sizable so I can see multiple months or allow a bigger view? All that effor to make a clock that I don't care about (why would I click on the time to show this to see an analog clock?). It's also so gray. Make it so the text is more readable.
In the Control Panel > Performance and Maintenance > Performance Center > Rate and Improve ...
If I had any misconceptions about the speed of Vista in a VMware instance, this clarifies the issue nicely:

In any case, I hope this isn't it. I realize Vista isn't done yet, but it's got to be better than this when it releases from a visual perspective. It's an improvement from XP, but nothing earth-shattering or even ground breaking. Just iterative improvement. Apple's OS X still looks better out the of box as an OS.