Since I haven't read Hunter S. Thompson's book, I can't judge Gonzo journalism or his writings, but I will point out my problems with this movie.

For me, "Fear and Loathing in Las Vegas" was nothing but 2 hours with two unlikable AND uninteresting characters doing all kinds of drugs. The occasional good moments and the reason why I don't give it an even lower rating happen thanks to the narration and an inspired, brief black-and-white footage from the 60's, the great soundtrack, plus Johnny Depp and Benicio Del Toro's performances (even though I could never relate to their characters, they fitted them perfectly). I can be fascinated by an unlikable character that I can't personally relate to when it's well written into a gripping character-study (as, say, Isabelle Huppert's complex Erica Kohut in "The Piano Teacher"), but that won't happen if they are also completely uninteresting and lack any sort of substance. People who consider the so-called "druggie lifestyle" a shock to the system and a form of artistic expression will most likely enjoy this (and there are lots of them, hence the major cult surrounding this movie), but I was bored or indifferent most of the time. Films like Dennis Hopper's "Easy Rider" (which didn't age very well in my opinion, but still keeps a rugged charm of 60's anarchy) and Danny Boyle's "Trainspotting" portrayed those "trips" and a whole generation without ever being dull. That said, I can see why some people love this movie... but if you have to dig such an empty "lifestyle" (hedonism? I don't think doing drugs all day long should be called that, sounds more like apathy to me) to appreciate it, then this is definitely not my cup of tea. 4/10.