... and it is definitely worth it! 4 and a half stars.
My biggest gripe is that they had to drop so much to make it a reasonable length movie. What I missed most was the various lessons Harry and friends learnt through the year, and as such the characterisations of the teachers were rather incomplete. There was also no reason I could see at all for dropping the potion puzzle with Hermione and Harry in the dungeon (it would have taken maybe 10 minutes of screen time). Apart from that, there was lots that would have been nice to see, but not missed so much.
Daniel Radcliffe has the distinct potential to be overshadowed by everything - even his own character. Fortunately, he isn't: I presume he must have been directed like that. Of the other characters, Robbie Coltrane as Hagrid absolutely shines ("I should not have told you that" :-). I thought Maggie Smith was a bit ordinary as McGonagall, which surprises me now that I think about it, but perhaps she didn't really have a lot to work with. Even in the books, McGonagall is not given much depth until the fourth book. Dumbledore, too, doesn't come across quite fully, either, but then his friendly and understanding attitude towards Harry at the end only hints at what he is like, again, something that only really comes out in later books. On the other hand, Tom Felton as Draco Malfoy really does not work. The effect is that Draco comes across as too much of a wannabe when in the book Harry, Ron and Hermione perceive him as much more of a threat. This, again, may be a case of simply not enough scenes for him.
Hogwarts itself is magnificent. Whilst it is hard to say it was what I imagined it to be from reading the book, I could certainly say it definitely does it justice. It and places like Diagon Alley give a delightful feel to how the wizarding world lives, and is one thing I like very much about the books. It is a curious mix of medieval with modern - witness Ollivander's wand shop, chock full of wands in cardboard boxes. Similarly is the students in wizard robes - over ordinary school uniforms!
Everyone comments on the Quidditch match. It was certainly very cinematic, but I felt not having seen Harry practise meant it lost something. But then, that would have been very difficult to put into the film.
It is tempting to compare HP with The Lord Of The Rings, but the two movies are intended to achieve different things. The most obvious difference is that the stories are very very different. A rather more subtle difference is that the role of magic is also vastly different. This does, in a way, exemplify everything that is different between the two. In the Harry Potter movie, magic is an everyday fact for people like Harry and learning how to do it is the point of Harry going to Hogwarts. In the Lord of the Rings, magic works very very differently and the story is one of ridding the world of a most dangerous magic. About the only thing in common with the two movies is the genre.
A reviewer on IMDB made the point that the confrontation with Voldemort seems to have overshadowed the fact that it was Harry's first year at Wizard school. This is a tricky balance. Rowling manages it very well in the novels and her involvement in making the movie probably helped make it work (I think) in the movie. IMO, movie makers will rarely do this, preferring to favour one story (usually called the "A" story) over the other (the "B" story). How Harry defeats Voldemort a second time is, I think, a very clever story device. If you've seen the movie but not read the book, then I can tell you that the explanation Dumbledore gives is pretty much exactly the same. (I can also assure you that Rowling finds a better way to describe it!)
I'm seriously interested in how well Warner et al bring the second book to the screen.
Wade.
PS. I have by now read all four books. Rowling gets better! If you found the first books un-put-down-able, you'll find the later ones impossible to stop reading! Harry Potter is top-drawer fantasy fiction.