Have not seen it. Why the R rating?

You must be kidding... Diana Ross is an icon in so many ways! If it weren't for this movie people would be saying "Billie Holiday who?"
She isn't trying to live up to a Jazz singer... She did release a Jazz album though called "Blue" and it sold really well on the jazz charts...
Diana isn't trying to be anything but Diana...

Check it out http://dianaross.ch/main/music/albums/albums.htm

This thread is not even about the merits of the film or its cast but about why it has an "R" rating. Since you have opened the window, allow me to contribute an opposing view. I agree with a lot of points that you raised concerning “Lady Sings the Blues”:
* It is not a authentic biopic on Billie Holliday but more a whitewashed version that made it more palatable for Middle-America.
* Physically Diana Ross did not resemble Billie Holiday or sound like her.
* The Louis McKay presented in the movie was more a composite of many different people in Billie's life rather than the authentic person.

Like you, I have watched the movie a few times but for me it was a pleasure. The first time I saw it was when it was first released in 1972 and I was barely 4 years old and it left an indelible mark on me since then. During this time, most of the films with a predominately Black cast were of the blaxploitation genre. You may think it strange or inappropriate for my parents to take a 4 year old to an "R" rated film but most of the films with mostly Black casts of this era were rated "R", mostly because of vulgarity and violence. My parents didn't expect me to fully understand this film and they assumed that I would probably sleep through it. Even at this young age, I was impressed to see a film on this grand scale that elevated a historical Black icon like Billie Holliday; this was unprecedented and this was not lost on me then or now.

I take exception with you saying that "this (is a) crappy movie...don't watch it." This is an excellent movie and by the rating it has received here (7/10) and the five Academy Awards & three Golden Globe nominations it garnered (Diana Ross won the Golden Globe for Most Promising New Actress); your opinion appears to be in the minority. While this film may gloss over a lot of Billie’s life, the script was based on her autobiography (this may be how Billie chose to remember her past) and the screenplay was also nominated for an Oscar.

Diana Ross did not capture the look and sound of Billie Holliday nor did she attempt to. Think about all of the other Black actresses they were considering for this role for the many years that this film was being developed: Dorothy Dandridge, Cicely Tyson, and Diahann Carroll just to name a few--all of these were Black actresses who could not sing nor did they resemble Billie either. Diana Ross did not channel Billie Holliday the way that Angela Bassett did with Tina Turner or the way Val Kilmer did with Jim Morrison or how Jamie Foxx did with Ray Charles but she internalized Billie’s triumphs, pain, struggles, and personal demons and depicted this very well and she interpreted Billie's voice by not trying to duplicate the inimitatable but maximized the range of her own voice using Billie's distinctive phrasing and capturing the essence of her spirit while coaxing out a myriad of emotions.

This film made me a Billie Holliday fan at age 4. After this film, in addition to Billie, I listened to Sarah Vaughn, Ella Fitzgerald, Mel Torme, Nat King Cole, Ethel Waters, and Dinah Washington while my peers were just starting to rock to disco (even though in my neighborhood we didn't call it disco--it was just R&B or dance music--disco was the name that others called it when they "discovered" it years later). This film still stands the test of time and judging by the success of Diana Ross’ last album, “Blue” (which was unreleased material originally recorded for Motown around the release of this movie) on the jazz and adult contemporary Billboard charts as well as winning a Grammy, your assessment that “Miss Ross…sucks” may be a little biased. Yes, Billie Holliday is without a doubt an icon but so is Diana Ross, no matter what you may think of her personally.

In conclusion, most reasonable people would have to admit that for a debut performance, Diana Ross did an outstanding job. In addition, for it to be the only screenplay that she has ever written, Suzanne DePasse (who was a Motown A&R executive at the time) created a great story even if it presents a slightly less gritty portrayal of the troubled singer’s life.