On the plus side, this film is wickedly funny. Bill Murray (an actor who has been both great and terrible in his career) does a phenomenal job as the acid-drenched reporter, bringing chaos into the lives of the rigid and pretentious. The plot is peppered with "respectable" places being dragged into mayhem, and "respectable" folks trying (unsuccessfully) to cope behind plastic smiles.
It even ventures into some higher themes, such as innocent kids being jailed by a heartless criminal system, and Thompson's own struggles between being a practical reporter and a fun-loving idealist (notice how Lazlo repeatedly re-surfaces just when Thompson starts to take on "real" jobs).
It's biggest fault, however, was that it failed to achieve any of the higher accomplishments of HST's writings. What makes Thompson such a powerful writer (to me, anyway) is the way he'll often turn on a dime and deliver stunningly sober dialogs on the human animal and where he's gone wrong. Nestled in the midst of the wine, women, and song are soliloquies that drive home a more positive message, and none of those made it into this film (in fact, no significant chunks of actual text from HST's books appeared at all). It's like they shaved off the surface 50% of Thompson's work and discarded the rest.
Compare this to Fear and Loathing, which was darker and more counter-cultural, and contained whole narrations excerpted from the novel. The latter perhaps has less appeal to the average viewer, but I'd think more to a Thompson fan.
All-in-all, this film is a light-hearted romp into anarchy, and worth watching. But if you've never actually READ Thompson, do so, as this movie doesn't accurately represent him.