DH1 suffers the most, in my opinion, from being half of a story, and half of a book. Most of the ambitious set-pieces and heroic derring-dos get pushed into the second half of the film, whereas DH1 gets saddled with all of the necessary plot set-up, as well as the part of the book that’s designed to emphasize the total hopelessness of our hero’s situation and the total dominance of the enemy—all leading up to the point where we get revived, figure out what’s going on, and get into things hardcore.
Unfortunately, I think the filmmakers got a little too into this section of the book and its insular atmosphere of desolate despair, and not enough into actually setting up the situation of the world at large. I think a number of scenes at Hogwarts, showing Snape as headmaster and the new state of the school under the Death Eater’s rule would have had a lot more emotional impact than seeing the same thing at the Ministry of Magic (which we’ve only seen since the fifth film, as opposed to Hogwarts which has always been a symbol of innocence and magic).
In addition, they also cut out one of the most effective passages in the book, where our heroes, stuck in the middle of nowhere, hear a broadcast from like-minded Anti-Voldemort people (Fred and George in fact) telling what’s going on in the world, speculating on Voldemort’s and Harry’s locations, and exhorting people to keep up the good fight. In the book, this scene is something of a watershed moment, the first time that Harry and co have gotten a real connection with the outside world and the life they’d led before all this happened, and inspires them to keep fighting. It would also provide a helpful break from the monotony and despair; but the filmmakers, alas, decided to cut it out.
And this ‘hunt’ isn’t very much of a hunt at all, as the filmmakers also cut out most of the scenes of them actively searching for Horcruxes, after the first one practically falls into their lap. Doing this would have added some more energy and ‘direction’ to things as well. And the plot and character meaning of these sequences, in which Harry becomes slowly obsessed with acquiring the Deathly Hallows (as something that will allow him to master death and so overcome Voldemort at last), leaving off the hunt for the Horcruxes, is also cut completely, leaving these scenes more meandering about than anything else.
Until finally, the death of Dobby (who died, in the book, because Harry’s obsession led them to get captured) convinces him to trust Dumbledore and not attempt to ‘master death’ in such a fashion, and he makes a conscious choice to let Voldemort have the Elder Wand, while he himself begins to plan the next heist of the horcrux. In the movie, though, most of this character stuff is cut out, and Harry just wanders around without doing much at all; and the death of Dobby just leads him to react again with grief, and make no important choice whatsoever, while the actual film ends with Voldemort’s triumph, without the character significance that this scene possesses in the book (Harry has already figured out where it is, could have gotten there before him, but has chosen not to out of trust for Dumbledore and in sorrow for his mistakes) totally absent.
In addition, the death of Dobby has a LOT more emotional impact in the books than in the films, as Dobby has appeared in the 2nd, 4th, 5th, and 6th films in some form, as a recurring character who helps out Harry when in need, and is endearing and ‘good’ in a way that few other characters have been. His coming to the rescue suddenly out of nowhere, when all hope has been lost, standing up to his former masters (the Malfoys) as a free elf, and then dieing a sacrificial death for Harry and his friends, is without a death the most emotional and touching death in any of the HP books, and the only one where I actually got choked up hardcore reading it.
In the films, though, like you’ve pointed out, he’s just a somewhat annoying character who appears only in the 2nd film as a nuisance and obstacle for Harry, then pops up 5 films later, appears in a few scenes, and promptly conks it. Much of the impact of his death is lost; though if you’ve read the books, too, most of this impact would have come through anyway, because of what you know about the character otherwise. This explains, I think, the vastly diverging reactions between hp fans and critics in this regard.
Don’t get me wrong, I still enjoyed the film; but I think it could have been done much, much better, and the cuts and changes from the book are done in such a way that, while most of the details are intact, the meaning and character significance behind them is cut out, leaving a film that appears meandering and convolving to people who don’t already know that significance.
However, I expect most film critics (and myself as well) will enjoy the second film much more, as it has two massive set piece action sequences, real heroism on the part of both main characters and recurring ones, a return to Hogwarts and a summing up of the entire series, and a character-driven confrontation and set of actions that should be much more emotionally-powerful and involving. Watched together, the first half will look much better, I think.
As a basic set-up to the second part, I think it will turn out to work quite well; as a stand-alone film, perhaps not so much.