On the contrary, I thought if anything it sped through far too quickly. However, that was necessary in order to fit in as much as they did. I thought it was handled very well.
However, I was disappointed the battle at the end was left out. They did that with Order of the Phoenix as well..... I wonder why?
And I actually left, commenting to my friend about how much more sophisticated the camera movement and cinematography was to the previous films. I thought they really stepped it up a notch.
As for too dark... hardly. I think if they spent too much time "faffing" as you say, then it's because they focussed more on the comedy aspects. Personally, I thought the amount of time they spent on comedy was a good idea - it was a nice balance of comedy and drama/horror.
Overall, I think the film was done very well. They managed to get in MOST of the key parts of the book (it would be impossible to get in everything). It seemed to have all the factors for a good film and the cinematography/direction had real style.
They had reasons for leaving bits of the book. They couldn't go into all that detail about horcruxes... it might have gotten really boring. They've got a BIG widespread market remember, including young children. And Harry not being frozen wasn't really a big deal. It wouldn't have come off on screen, that's for sure. They have to make cinematic decisions remember.