First things first: Victor Hugo's novel is 150 years old, and the Boublil-Schonberg musical is 30 years old, so let's not pretend that we need to avoid giving away plot points on this one. I'm not going to go out of my way to gratuitously mention things, but I think a century is well past the statute of limitations on spoilers.
Hugo's story, even in its purest form as a novel, carries so much emotion, sentiment, and melodrama that it's starting to stagger under the weight. Pile on a sentimental and melodramatic score, and the musical version walks right up to the edge of camp.
So the last thing Tom Hooper needed to do was direct the movie in a style that adds on even more emotion. The movie, despite a few marvelous moments, is washed away in a sea of tears, so intent on pummelling us with its characters' every twinge of grief and misery that there's no room for us to feel anything.
The use of sustained extreme closeup doesn't help, especially given Hooper's choice to encourage his actors to flamboyantly overdo the tears and the sniffling. We don't normally look at people at such a close distance, and when they're crying, our instinct is to pull back and allow them some personal space. So when Anne Hathaway blubbers her way through "I Dreamed a Dream," or when Eddie Redmayne weeps out "Empty Chairs at Empty Tables," we want to get away; we're invading on moments that are too personal for our presence. And since we can't get away, we start resenting the movie for forcing us into these moments of emotional violation. (And that doesn't even address the fact that the blubbering and tears make the singing less effective, and the lyrics harder to understand.)
The movie's most successful moments, therefore, don't necessarily come from its best singers, but from its most understated. Russell Crowe doesn't have the best voice in the cast (though I think he's perfectly fine in the role), but his restraint and lack of sobbing make the moments leading up to Javert's suicide the most moving in the movie. (I could, however, have done without the resounding CRACK that Hooper throws in as the body lands; the point would have been made without the cartoonish sound effect.)
Get past the "please cry for the camera" direction, and most of the cast is quite good, with voices well suited to the roles. Amanda Seyfried squeaks a bit on her highest notes, and "Bring Him Home" has always been pitched far too high compared to the rest of Valjean's music, so Hugh Jackman is at his worst there, but those are minor flaws.
The biggest casting problem comes with Sacha Baron Cohen and Helena Bonham Carter as the Thenardiers; the one thing that comic relief characters must be is funny, and these two aren't. Baron Cohen can at least carry a tune, but "Master of the House" is staged in so sluggish a manner that the comedy never comes through.
And for all the bad directing choices, the movie has its moments; there is a stretch of about ten or fifteen minutes late in the movie that is thrilling. Samantha Barks as Eponine sings a lovely "On My Own;" the "One Day More" ensemble, which has always been the most effective number in the score, works beautifully; and even though we can't understand most of the choral lyrics, "Do You Hear the People Sing" is staged with great power.
Had the rest of the movie reached that level, it would have been a glorious success. As it is, it's a movie that so badly indulges -- hell, not merely indulges, but wallows in -- the biggest weaknesses of its source material that it becomes an unrelenting, intolerable scream of "FEEL MY PAIN!"