First a little hiccup: The installer – it’s a nice feature… but why?? 99% of the developers using Sitecore, doesn’t need the help it provides. Sometimes it seems like the Sitecore guys get an idea, and totally forgets about the target audience.
In my case, the installer meant that I tried to download the Beta 3 times, and I finally had to ask support for a zipped version (which they provided pretty fast). The problem was that I’m using a Danish version of Windows XP, and the installer was looking for a user called “Network Service”. Well – on a Danish Windows XP the user is called “Netværkstjeneste”… Grrr… (the zipped version took about 3 minutes to setup – including moving files around).
Ok – now I’ve got that out of my system, lets look at the system:
Sitecore 5.3 Beta UI 
“Beta First Impression”:
WOOOOWWW!! It’s fast… If you compare it to 5.1 its beyond compare. Even on my small laptop!
Opening the Content Editor the first time still takes about 5-10 seconds but after that it works really really fast. The first thing you notice is that they’ve fixed some of the UI-annoyances in 5.1/5.2. The HTML-field load behaviour (Grr...) has gone, and there is no more waste of space. Brilliant!
Space in 5.2 compared to 5.3:
Contextual tabs:
The “Contextual tabs” toolbar is very intuitive. You use 30 seconds to get the idea, and then you are cookin’ (well done Microsoft ;o)).
The Media Shop:
In 5.3 all media is placed in the database as blobs – great idea. I’m looking forward to see what possibilities it generates… Also – Sitecore extracts the essential Exif data. This can prove to be very useful in the future.
Media shop Exif data 
The Template Editor:
The template editor has got a long needed overhaul. It’s much better than 5.1, but we’re not there yet. The main reason its better (I think) is the increased speed of the Content Editor. You still have to save each time you create a field/section, and sorting fields is still a hassle. It still leaves me longing for the good old 4.3 days… ;o)
However – it’s a step in the right direction…
Template Editor 
The Developer Center:
It looks ok, but – honestly – I’m not sure I’m gonna use it that much… I like the Xpath Builder though.
The Developer Center 
Other things:
It looks like Sitecore has improved a lot of small things throughout the system. For example: The Publish dialog now has a checkbox to always skip the annoying first page:
The publish dialog 
Conclusion:
Well done guys! You’ve listened to the target audience (except the installer issue), and it looks like 5.3 is going to be the best version yet of the worlds best CMS… When the system acts and performs like this, it leaves you wanting more.