Well the channels you get in HD are as follows ~
BBC HD
Living HD
4 HD
FX HD
National Geographic HD
MTVN HD
ESPN HD
The boxes themselves are a bit better looking,more modern and stylish I suppose,they have more functions of course,due to it being HD box one of its better features is the ability to record from two different channels and watch another all at the same time ...the HD pictures can be outstanding on some channels (notably for me) on Nat Geo in some of their documentaries its almost like watching in 3D...not all high definition is what you would expect it to be though (I have found) ...
It takes a couple of days to explore the box of course but Im sure you will like it once you get used to it,not much of a user manual supplied with it,but instructions are available on screen via the help section ...
Im sure you will enjoy it
wish you well ......