I never really thought much about Russel Brand and well the media hates him so they don't want to give him much time either. Apparently he has a very popular and insightful podcast that I have never listened to... whatever, this movie is lots of fun and i love it.
This film is a sort of a spin off for 2 minor characters that appeared in Forgetting Sarah Marshall (another film worth seeing.) I bet this was a tough sell to the producers that decided to make it because Jonah Hill's character in Forgetting Sarah was so minor that I don't think he even had a name. I'm happy whoever managed to convince them to greenlight this project is such a great speaker because I love films with funny, yet good music mixed in and that is precisely what this is. The music in the film is by a collective effort called "Infant Sorrow" and Aldus Snow genuinely sings all the songs in the film (and on the album.)
So the story is like this: Aaron Green (Jonah Hill) is a talent scout for a mid-sized record label, the one that currently represents Aldous Snow (Russel Brand) whom Aaron considers a magnificent but fading talent due to the Aldous' recent release of a terrible and insensitive track. Aaron convinces his boss to put on a massive concert for Aldous as he is "the last remaining rock star." This will take place at the Greek Theater in Los Angeles and Aaron has been tasked with making certain that Aldous gets to the show, at the Greek, on time. Now you understand that name of the film.
There is just one problem: Aldous is a millionaire party-boy who doesn't listen to anyone and although he means well, he plays the world by his own rules, which makes getting him to L.A. a very difficult, but exciting task. The situations they end up in are ludicrous of course but the movie would be less fun without them.
There are a number of promotional gigs that they have to perform along the way and Aldous is too trashed to remember the lyrics and other such things that result in us hearing fantastically silly songs like "The Clap" (seriously, if you are a native-English speaker and understand nuance of the language these songs are hilarious.)
I don't know if you are aware of this but Russel and Jonah are actually really good actors (I think that Jonah might be one of the best actors alive today) and their chemistry in this film is spot-on. I think that a vast majority of the public also enjoyed this movie because it doubled its production budget and received mostly positive reviews. Of course the SJW's briefly tried to ruin everyone's fun by protesting one particular scene but thankfully they failed. See this.