I am not a huge musical theater buff, but I do enjoy and have some very strong opinions about how it should (and should not) be done. I also had never read the book nor seen the show, so this was my first experience with it.
I quite enjoyed the movie. Some of the main characters were pretty weak singers (notably Amanda Seyfreid and Russel Crowe), but even then, I didn't think there performances were terrible.
As a professional audio designer, I appreciate that this film is basically the kind of thing that sound guys wait their entire careers to work on (even guys who regularly do big budget films). The singing was all recorded live, on-set; there was no lip syncing. And to my earlier comment about how musicals should not be done: my #1 complaint with musical theater -and the thing that keeps me from being a true fan of the genre- is that the production is frequently unnecessarily cheesy to the point of being distracting. And even if it's not cheesy, it's too slick and detracts from the seriousness of the subject matter. This movie did not do that. At all. In fact, they took pains to avoid that: Anne Hathaway's "I Dream A Dream" is a single, unedited 3-minute close-up, and there's not one drop of reverb anywhere. There were a couple of very brief moments where it flirted with cheesiness: a couple were nods to the theater buffs (before Fantine sells herself, I thought the prostitutes looked kind of cartoony, like you'd see on stage) and a couple were just strange choices for camera angles, but other than that, it was spot-on.
But even the weak singing worked to the film's advantage at times. Crowe's Javert was pretty flat and one-dimensional, but his singing had a gritty, strained quality that lent itself well to some of the hatred and conflict he's expressing.
That's not to say that all of the singing was bad. Marius, Eponine, the revolutionaries and ensemble are FANTASTIC.
Valjean's death scene was wonderful. I can say without exaggerating that the entire theater was audibly crying.
So, to answer your question: whether you should lower your expectations depends on what you're looking for. I have a bunch of friends who are in the theater and their opinions are mixed (let's just say that they're a little harsher on the singing). While I don't think they're wrong, I do think that was more than outweighed by the other creative decisions that were made, which supported the weight and emotion of the material.
-Dan.
