The first film remains my personal favourite for the reason that it is the one that stands out best as a stand-alone film. The first year at Hogwarts is the most innocent for Harry and he has yet to experience the true danger that would appear in the later films.
The innocence is further elaborated by the fact that this is the only film in the series made before the actor’s voices deepened due to adolescence.
Speaking of the actors, when the first came out, I did not believe that they would manage to adapt all seven books in the series (three of which were not yet published) and keep the cast at the right age. Now, the series is poised to end in 2011 (ten years after the release of this film) and the only major cast member to be replaced was Richard Harris, who died after the release of the second film.
It is for this fact alone that Harry Potter will go down as one of the best adaptations of a book series.
10/10