As a longtime fan of Motley Crue harkening back to my middle school days -- fan in the form of nostalgia, not necessarily hardcore contemporary fandom, it was with a mix of curiosity and genuine interest that I watched this on the day of its premiere.
On the whole, I thought it was nicely done -- it's not Oscar caliber, but the script, the acting and the period vibe were all on point. In particular, I thought the actors portraying Vince Neil and Tommy Lee did a great job. And, overall, having seen countless interviews of Motley Crue, all of the actors did a great job nailing their character and the small nuances that added up to a suspension of disbelief.
The detail in the movie for the trained eye was also nice. For example, in the post-Dr. Feelgood era when Vince left the band and John Corabi joined, there's a long shot on the exterior of a recording studio and Peal Jam's album cover for 10 is plastered on the outside. It's a small detail, but it tells the viewer that, yes, this is the Grunge era where Motley struggled with their footing.
Overall, thoroughly watchable, thoroughly enjoyable and a recommended flick for even the casual rock fan.