Go see. This weekend.
I saw it last Saturday (paid preview at Harrogate Odeon), and really enjoyed it. I’m a huge fan of the books, and was deeply impressed by the translation to screen – with the sole exception of Richard Harris as Dumbledore, who was very disappointing.
Of course, loads of the book was missed out, but pretty much everything essential was there (except for the life-debt thing between Snape and James Potter?!?!?), and the special effects where just as they should be in a film – ie seemless and un-noticeable.