This great film and novel adaptation is obviously underrated.
Although I have not read the book, (and nor should I to be able to personally judge this film), my guess is that probably most people are whining that the book was better. That's like saying that the car was better than the bike. They probably complain that the movie was not a precise enough adaptation. When will people realise that an exact adaptation will usually result in a boring and overly long film?. The movie definitely has the essential qualities for a good film with it's intelligent script, compelling drama, sober realism and superb acting.
This is Michael J Fox's best role and he does a great job. I think he's such an underrated actor, he made Family Ties what it was and will never be forgotten as Marty Mc Fly in Back to the Future, but this is his peak film.
I could very much symphatise and identify with the main character that slowly loses grip on reality, eventually spending most of his time in a drugged state of mind. Drugs are his only joy, until he's finally confronted by his caring brother and becomes at peace with reality in a moderately positive ending (which was criticised by some). His loneliness and desperation are depicted in a very convincing way, with his heartless girlfriend (Phoebe Cates) and harsh boss. My favorite scenes are the ones at work, where his incompetence becomes painfully evident.
Having recently watched Requiem for a Dream (also about drug addiction), I realize this movie's even better. 9 out of 10.