Carol and I went to see The Producers a few days ago. This version (the 2005 version, starring Matthew Broderick and Nathan Lane, not the 1968 version starring Zero Mostel and Gene Wilder) is a successful film adaptation of the musical adaptation of the film about the production of musicals, and if that's just too confusing, I'll point out that it's darned funny.
When I went into the theater, I was a bit concerned, because I truly enjoyed the original 1968 version of this now-classi Mel Brooks film.
I will warn up front that if you're over-sensitive about movies that make fun of war, Hitler, and the NAZI party, you'll probably have some difficulties with this film.
In comparison with the original film, which was not a musical, but a film about a musical, this film covers less of the back story and doesn't concentrate as much on the production steps of the musical (including the auditions and rehearsals), however the addition of some nicely-staged musical numbers makes it a nonetheless entertaining adaptation.
For people inclined to like Brooks's sometimes-offensive, always-blunt, over- the-top style of humor, I'd suggest seeing both of the films.