As a professed lover of musicals, it does me good to see that this art form is being revived in film. This does not necessarily mean that every movie that comes out with singing in it has my blessing. Recent films such as The Phantom of the Opera, RENT, Sweeney Todd, Hairspray, Chicago, and Mamma Mia! have put musicals back into the public eye, giving them a wider popularity. But that doesn't mean that this is entirely a good thing for every great musical to make its way to the screen.

• Exposure- It gets musicals out there and gives the opportunity for people to see the shows who would not otherwise see them. Some people who live in sparsely populated areas would never have the opportunity to see these shows on stage, so the film gives them a chance to experience them. And some just don't know about these shows until the film version comes out. Either way, it gets the word out about a story that may have enjoyed popularity and success for decades before. And it's really pleasant to be able to discuss my favorite shows with a wider group of people. Plus, with greater exposure, fewer people give me odd looks when I wear my t-shirts from the Broadway shows I've seen.
• Budget- There's so much more you can do in terms of the scale of the productions when it's on screen.
• Medium- You're not confined to what actors can physically do onstage. You can add settings and props and stunts and all sorts of fancy editing to carry off something that would never work on stage. It's much easier to convince the audience that the setting is creepy dirty London in Sweeney Todd when they can actually depict dirty creepy London through CGI. Likewise, filmmakers don't have to resort to theatre tricks to convince you that the Phantom is haunting the Paris opera, and they don't have to stylize the death of Angel in RENT (not that it's pleasant to watch him wasting away, but it clears up some confusion for the less-artsy audience).
• Orchestrations- On stage, you only have a few people stuffed in an orchestra pit putting out all the sound. And while they're usually very good, they can't compete with the 90 piece orchestras that perform the film soundtracks! Plus, composers tend to bring out some additional fun stuff for transitions when their shows make it to screen. Personally, I prefer the Mamma Mia! film soundtrack (despite Pierce Brosnan's singing and the way it hurts my soul) because of the wonderful orchestrations- Benny and Bjorn had fun with this one. And I really enjoyed the additional music Lord Webber added for movie Phantom, although I found it out of place and vastly different from the rest of the piece.
• Big names- While Broadway and the West End attract some big stars, where else are you gonna find Meryl Streep in a musical?

• Actors- Most of the time in the contemporary musical film, the casting is in favor of those who look the part or are younger and hotter, as opposed to those who actually can sing or have experience with this art form. Believe me, as a diehard fan of Phantom, nothing is more painful for me than listening to my angel of music growl and strain like a chain-smoking rock star instead of an operatic genius. This isn't always the case; RENT was made with almost the entire original Broadway cast, and look at how well that turned out.
• Editing- Some musicals get cut to pieces to make it to film. Most of the complicated songs were cut out of Sweeney Todd, and most of the songs that remained were still really watered down. The some characters changed in A Chorus Line, Cabaret lost lots of its original music, as it was made instrumental background music.
• Interpretation- A new director working with a new cast with all their unique gifts is going to interpret the show differently and portray it differently from its original incarnation. The result? Angry Broadway fans. Believe me, when I saw that they'd cut all the mysticism from Phantom, I was cursing Joel Schumacher.
• New fanbase- That's right, all that exposure will attract fans sporting the shirts and designing the avatars who have never witnessed the true scope of the original work. I had a girl try to correct me on some facts of the RENT story my freshman year of college...she unwittingly unleashed the wrath of a longtime Renthead. And if one more person tells me that Christine never loved the Phantom, I'm going to have to send Joel Schumacher all the hate-mail I've accumulated since 2004.
• New performances replacing the old ones- There's something magical and beautiful in a Broadway diva or leading man creating a powerful role that you know will be remembered forever. So it's really really sad when the new incarnation erases the all the hard work and creativity. I love Johnny Depp, but his Sweeney doesn't touch George Hearn or Len Carinou. And God knows that Patti LuPone and Angela Lansbury's Mrs. Lovett could eat Helena Bonham Carter's for breakfast. Besides that, you really don't want something as wonderful as say Jerry Orbach's performance in Chicago being lost to the likes of RICHARD GERE.