I worried a lot about Chicago as a movie. It's a fun play, and the music is great, but the book is shallow, at best, and none of the characters have enough depth to translate to the big screen. It was really an all-singing, all-dancing Bob Fosse blowout, criticized at the time for not even having enough story to be a really good musical (and that is saying something). Add to that the (to me) unpleasant prospect of Rene Zellweger, in all her anorexic glory, as the lead, and I got a big case of the "this is a bad idea" willies.
Turns out, Chicago is a damn fine movie -- one of my favorite of the year. In a shrewd move, the screenwriter placed all of the musical numbers as daydreams in the characters' heads, beefed up the book a great deal, and tacked on an extended ending, with an additional number (during which Richard Gere does an amazing tap dance). The end result is an incredibly engaging, well-crafted, virtually seamless movie musical. The only really loose screw is in Queen Latifah as Matron "Mama" Morton. She's a pioneer in the hip-hop industry, a great singer, and probably a good actress, in the right role, but she just wasn't up to the dominant, controlling, and often super-sexually aggressive presence the role calls for.
While I won't vote for Chicago for Best Picture, it's only because a handful of smaller films (and the Two Towers) really blew me away this holiday season. I would urge you, whatever you think of the idea of movie musicals, to go out and see this one. I really think you'll love it.