Great points, Majestic. Personally, I feel that POTO was the worst of those "big 3" musical films because of its OOC portrayals of the main characters and its apathy or borderline contempt for the novel, the stage show, and French history. But I can see where you're coming from re: Sweeney,
as well. I enjoyed the film when I first saw it (and still kinda do), but that's mainly because of the things I adored in the original show that the film didn't mess with too badly. The cutting of ensemble numbers bothered me quite a bit, though -- I could sort of understand Burton's rationale for nixing the "Ballad" sequences (though I missed those most of all), but cutting the ensemble's lines in "Pirelli's Miracle Elixir" and "God, That's Good" struck me as really unnecessary, especially since that resulted in the latter song not having its title come up at all.
What worried me after that was some of the fan reaction. On a few musical boards I frequented, there was some chatter about how ensemble numbers were now "obsolete" in musical films, and future projects could cut all such numbers because of how well these fans thought it worked in Sweeney.
I'm thankful that subsequent musical films didn't follow that precedent, especially LM -- I don't even want to think about what the film would have been like if the creators had done that.
Getting back to LM, though... I did have one issue with the way the ensemble was used. In some of the scenes with Les Amis, they come across to me as a homogeneous mass rather than a group of characters with distinct personalities. I think this is at least partially because so much stuff with them was cut, and also because they sing DYHTPS and other bits as one unified group rather than individual members getting their solo sections like in the stage show. The cinematography didn't really help there, either -- die-hard fans like us who know the Brick really well and can identify individual Amis in the stage show had no problem, but those who haven't read it recently (or at all) likely wouldn't notice the boys' mannerisms and character-appropriate attire, and also wouldn't have any clue why (for example) the camera was focusing so much on this seemingly random, unnamed woman helping the Amis prepare in "One Day More." I myself confused Courfeyrac and Grantaire, and found myself wondering why 'Fey was coming into the Café at the end of the battle (especially when I was sure that I had just seen him die shortly before). It wasn't until he stood next to E that I realized he was R.