You may say to yourself, "Don Johnson as Elvis? Can that work? Is it possible? Seems like an terrible choice to me, but perhaps I should have an open mind. Maybe I'll be surprised. Maybe he can pull it off."
NOT!
Don Johnson is not a bad actor. But he is an awful Elvis. He's too short, too weak-voiced, too sharply featured ... well you've already imagined how bad he would be. Add to that a hokey black wig and heavy-handed eye-liner and mascara and it's a big fat embarrassing mess.
The best I can say is that since Johnson's acting is decent and since his impersonation is so far off, after a while you don't even think of him as Elvis anymore. You see him as some other crazed pop star instead. Then, on that level, the movie becomes watchable.
Stephanie Zimbalist is also not ideally cast as the tall, beauty queen, Linda Thompson. But she is attractive in her own right and plays the part with the honesty, elegance and intelligence we've come to expect from all her roles. There may be too much intelligence in her performance. You have to be kind of a dope to stick with a dope abusing dope.
There's nothing new to this story; we've heard it many times before. If you've looking for new info or insight, you won't find it. It's told as a love story - an unrequited one: Linda for Elvis and Elvis for drugs.