Renee Zellweger does an excellent job as Judy Garland but, using her own voice, shows that there was only one Judy Garland! Judy Davis, in 2001, did a 4 hour TV story called "Life With Judy Garland: Me & My Shadow", winning an Emmy, but lip-synced Judy's voice and was more effective.
In "I Could Go On Singing", Garland's last movie, the screenplay did a much better job about a world famous singer showing the love for her children then this screenplay by Tom Edge based on a play by Peter Quilter. The flashbacks to Judy's start and her treatment by the studio, especially during "The Wizard of Oz", along with 'appearances' by actors such as Mickey Rooney, doesn't add anything new.
More time spent with Judy's ex husband, Sid Luft (Rufus Sewell) and Jessie Buckley, as Judy's last assistant, Rosalie, would have added more to the story about her last days. Finn Wittrock, as Micky Deans, her last husband, for less than a year and rumored to be gay is given less attention but then another husband Vincent Minnelli, father of Liza and also gay, isn't even mentioned. Darci Shawn, as young Judy, would make perfect casting as a young Liz Taylor.
"Judy" delivers one fine performance and a tearful last 5 minutes but instead of recommending seeing this I would recommend you seeing Judy Garland in "I Could Go On Singing" and Judy Davis in "Life With Judy Garland: Me & My Shadow".