I'm not a big fan of the 2004 movie. I found the acting to be pretty wooden from nearly everyone -- it seemed like the only ones who were making much effort there were Gerard Butler and Minnie Driver. I agree with Taelin and Gervais about Patrick Wilson as Raoul -- he, the director, and the composer all said in one way or another in various interviews that they didn't care much about the character, and it showed in the movie.
As for the singing... I'm not a huge stickler for vocal quality in musical films, but the way the script built up the Phantom and Christine as having divine, angelic voices made the casting in the movie more than a tad unbelievable for me. When Christine is getting stupendous applause despite having a voice that realistically wouldn't carry past the first row or two of the theatre, and when the Phantom is described as being an angel of music despite sounding just slightly better than your average Joe at a karaoke party, that kind of destroys the illusion for me. And on the flip side, the movie also goes out of its way to make it seem like Carlotta is a horrible singer, even having stagehands stuffing cotton in their ears when she starts to sing, when the character actually has perhaps the best voice of anyone in the cast (and yes, I know the actress was dubbed). When it comes to things like that, I actually find it easier to suspend my disbelief when seeing performers who aren't necessarily the best singers playing these roles in a stage show compared to a film.
The biggest issue for me with this movie, though, was that the director didn't seem to care all that much about the story or the characters. He cast actors who were, in his own words, "young and sexy" for the main roles rather than choosing performers with the kind of acting and singing experience required for the parts. He didn't seem to pay much attention to the novel or to the real-life historical events that made the novel's Phantom somewhat plausible. The movie tried too hard to humanize the Phantom and explained away his "magic tricks" in a way that didn't make him seem like much of a genius -- the novel, by contrast, also explained a lot of his tricks, but the secrets behind them did require a substantial amount of skill and outside-the-box thinking on Erik's part to pull them off. And the toning down of the Phantom's deformity felt a bit condescending to the audience in my view; it was like the director thought the audience wouldn't sympathize with someone who was too ugly, and so he made the deformity into something that looked like just a bad sunburn/allergic reaction.
In any case, I don't hate the movie, and I did enjoy rewatching it sometimes. The foreign-language dubs were pretty good as well, and fixed a lot of the problems I had with the vocal performances. But now that we have the 25th anniversary concert and YouTube clips of various live productions, I usually turn to those rather than the movie if I want to see Phantom and can't get to a live show.