I just came back from seeing it...
...and I adored it! It was heartbreaking, thought-provoking, emotive, really the greatest Harry Potter film of them all. Snape's death scene was filmed with such emotion and attention to detail, it was really fantastic. I wish they would have included the part where Harry finds the first half of Lily's letter to Sirius and a torn picture of himself as a baby and James in Grimmauld Place, and later discovers through Snape's memories that the missing half of the letter and picture (Lily's signature and "love", along with her picture) was in Snape's possession all along. Overall, the whole pensieve sequence could have gone much better, really expanding on the later years of their friendship, showing how her romantic attachment to James Potter caused them to drift apart, and really shown how much of a lowlife jerk (and he was) James had been to Snape throughout their entire Hogwarts career. Even with all that, however, Snape's loyalty to Lily never faltered, and although he had a bit of disdain for Harry, he protected him from the shadows since they met so that Lily's sacrifice would not be in vain.
I really do think the Harry Potter series is a rarity among contemporary fiction, especially among children's literature, which often tends to work in terms of black-and-white good/evil, win/lose, etc. I think the Harry Potter series presents life in its most realistic manner--there are no wholly good or evil people (even Dumbledore, a highly respected wizard thought to be the antithesis of Voldemort, had a dark side and a manipulative streak [i.e. manipulating both Harry and Snape, presumably "for the greater good," as his old friend Grindelwald would have said]. By the same token, Voldemort himself was not born a monster--he was denied love as a child, and the bleak circumstances under which he developed permitted his pathology to progress and proliferate into the self-destructive madness it became at its zenith. Thus, we are able to understand how this came about, something which is not often explained in children's books, which typically read like nationalist history books with the good guys' being bloody perfect and the bad guys being just plain evil, period). Similarly, there are no "total" victories--the novels have many Pyrrhic victories, among them the Battle at the Ministry of Magic, which results in Sirius' death, and the Battle of Hogwarts, which results in the death of Remus Lupin, Nymphadora Tonks, and Fred Weasley, among others. I think that's important for children to understand--the concept of sacrifice and the reasons why people do it.
Snape was arguably the best person out of all the adult characters. Although he could be cruel at times [most notably to Harry, at whom I think he projected his image of James, even though the two were nothing alike--if anything, Harry really resembles Snape more than he does his father, in regards to personality]. Yet, even despite this minor flaw, he always knew where his loyalties were, and sacrificed everything to protect the child of a man who tormented him for his whole life [the Marauders were total b--tards, let's face it] for the woman he loved. Moreover, he could have easily turned Sirius Black in without causing any real damage to the Order or danger to Harry (and justifiably too, as much as I love Sirius, he was a total b--tard to Severus), but he never did. I don't think one could say something like that of any of the other adult characters (Remus Lupin, for example, was the "idle bystander" of the Marauder bunch--refusing to wholly partake in their bullying, but failing to report any of it to the proper school authorities for Snape's sake). They all seem to be very set on protecting their lot and don't particularly care for protecting anyone else, especially not people whom they consider enemies. The only other characters I could think of who ever displayed altruism towards people they disliked are, interestingly enough, Draco Malfoy [saves Harry by not giving him away at Malfoy Manor, even though exposing him could have brought him great rewards] and Harry [saves Malfoy twice in the Deathly Hallows novel].
With that said, I absolutely adored the film. I cried at Snape's death scene, something which I seldom do. It is a rare occurrence to see me cry, and even rarer that a film would evoke such emotions in me. However, Snape was an extraordinary being in an ordinary world, a true hero and arguably the bravest of them all (along with Harry). I've been in love with his character for ages now, really, in love with the whole series--it is a gem among the mud that is contemporary fiction. Every time I read it or watch the films, I experience something truly fantastic. It is art at its finest, ingenious for its time, just truly amazing.
My one issue regarding the films, particularly Order of the Phoenix, was with the way they filmed the scene of Sirius' death. I think they should have brought more emotion into it--after all, he was virtually Harry's foster father (similar to how Molly Weasley is sort of his foster mother). Another thing they should have really addressed was Percy Weasley's realization of his errors and subsequent reconciliation with his family at the death of Fred Weasley--they left that loose end untied.
Overall, though, the film was fantastic. It truly did justice to the greater concepts of the final book.