Some of the button sizes has been increased. The start menu has been gotten rid of in favor of a full screen App menu.
Overall it's more finger-friendly.
I, however, don't like the new interface in comparison to the TouchFLO 2D interface (HTC Diamond interface). It is an improvement if you like the standard 6.1 interface and hate TouchFLO 2D.
My favorite thing about the TouchFLO interface was the quick contacts menu, because it made it easier to call the core set of people I call often.
WM 6.5 is STILL hard to use as a phone