Although the film opens with Rick Allen's accident and then flashes back from there, it doesn't overly dwell on just the negative. It makes it clear that these were stand-up guys devoted equally to their friendship as to their music.
And even though the actors were obviously chosen based on their strong physical resemblance to each band member, all of them give really strong performances. They all come across as real people, and not at all as mere hired lookalikes. And even though the role is severely limited, Anthony Michael Hall gets the gist of producer Mutt Lange's role (although they made him American when he's actually British).
A few time-line errors: They show the band working on Pour Some Sugar on Me while Rick is in the hospital and before Mutt Lange rejoins them in the studio. In fact, Sugar was the last song on the Hysteria album to be written and it was in fact Lange who recognized it as a potential smash hit and insisted on its development & inclusion (even though they were already way behind schedule).
Also the final concert scene where Rick plays live again for the first time, this was actually at an outdoor concert in Germany. But there actually were people grumbling about a "freak show" in reference to a one-armed drummer (not fans, but members of another band that was also playing that gig). It does also accurately portray that Allen performed without a hitch that day and was warmly welcomed back by the audience.
The real members of Def Leppard themselves have gone on record saying that even though they had no input to it, overall, they were reasonably satisfied with this docudrama.