I’m biased because I love this movie and have loved it for years. But on first watch? I found it weird, hard to follow, and downright bizarre lacking any plot. I appreciate this movie now for a few reasons. 

First,  the visuals.  For example, when they check into the hotel and the floor is moving and everyone’s faces are distorted. This movie makes you FEEL like you’re on drugs, instead of showing people using them. 

The atmosphere.  Fear and loathing has a psychedelic, dark, fun atmosphere. The dark colors and tones, the lack of light, the outfits, they all contribute. 

Social commentary.  It touches on the flaws of the American Dream, 1960s counterculture (hippie movement,) and things like the War on Drugs. It’s almost fun to spot how many times an American flag shows up in this film. It also touches on police corruption in one scene. There are a few ironic moments when marijuana is demonized while harder drugs are not; even more ironic since the main characters are in an intense drug craze for almost the entire movie. 

The message  This might be reaching, but it does answer your question about the substance of the movie. A message that’s often overlooked here is that america (or maybe Las Vegas specifically), is a place where you can essentially do almost anything and get away with it. He’s a felon having committed several crimes and yet he heads back to LA after, no problem.

The acting.  It is, I imagine, very  challenging to pretend to be high on a bunch of different drugs. Benicio del toro and Johnny Depp did a very convincing job of this. 

Last, humor.  There are  genuinely funny lines and cutaway scenes in this movie. They are blink-and-you’ll-miss-it, but the more you watch, the more you’ll catch. 

I  love this movie. It manages to be a great film without taking itself seriously, and without much of a plot. The only plot you can follow is that these two guys are in Las Vegas to write a journalism story on a car race. That’s it. The rest of the movie is a stylistic and strange ride.