Ok, I finally got the monkey off my shoulder and finished Portal 2
Now the entire time that I was playing the game I thought "Well it's good, hell some parts are better than Portal, but there is just no way it could ever be better." And then I got to the end. And all I could say is ". . .", and then my brain decided that it would work again and it was "Ok I take it back it was amazing"
It is rather hard to describe how Portal 2 surpasses the original without spoilers. So to keep it short. The puzzle mechanics have increased tremendously it differs very much now, and eliminates most of those reflex orientated puzzles.
The area where Portal 2 truly shines is story. Portal never had much in terms of a story -although I enjoyed it greatly- Portal 2 explores areas that we never knew existed, and wondering how it factors into the Half-Life universe as a whole is puzzling. But that just leaves me wanting more from Valve.
Oh yes the ending of Portal 2 is far better than the original, except the theme song. I don't believe there can be a better song than Still Alive.
PS: In retrospect I realise that I could sum everything up by simply saying. Portal 2 is a most worthy sequel to Portal.