This new version of the Web Apps works on tablets too such as the iPad or, in the future, Windows 8 tablets.
At the moment all of the Web Apps, especially Word, only have basic features. That might be because it is still a preview or that Microsoft don't want to be giving you their best quality service for free (my guess is the latter).
Like the old version, it gives you the option to open all the online documents on the Microsoft Office you have on your PC.
And to be honest with you, I don't see that much change from the old version of the Office Web Apps. I can see Microsoft has changed some of the fonts and a bit of the layout however there are no brand new features which stand out to me which is disappointing. I will say again though that this is only a preview and when it is officially released in a few weeks/months time it might include many more feaures because unless they do, I'm extremely disappointed.Maybe the only point of Office 13 Web Apps was to test if they actually could make a version of Microsoft Office which will work on tablet computers. I just hope that the desktop version of Office '13 is a lot better.