I'm at work so it isn't prudent to play with it too much, but it's now the builder on Wizards.com
It requires a Silverlight Plugin from Microsoft, but at least it will now work on Macs... I'll have to test at home if it will in firefox on Ubuntu.
I'm sad to see that the Essentials Assassin isn't an option.
Also, the Essentials classes only work with the Essentials races, feats, and limited gear.
Essentials Feats & content, on the other hand, are available for all characters.
Anyone had a chance to play with it in more detail yet?