Instead of repeating stuff you can read in the official documentation, I will just leave two examples of how different is the new model:
And allows compose assertions too:
Assert.That(myNumber, Is.GreaterThan(0) & Is.LessThanOrEqualTo(5));
And, continuing with testing, another great tool I expect to use soon (maybe in my next work assignment ;), WatiN has released the 1.1.0 version.
Apart from being quite usefull (web application testing has been quite painful until last years), it can be integrated in NUnit too (sorry MS guys, I still prefer CC.NET/NAnt before VSTS).