I like the premise of The Rocker so much -- middle-aged wannabe rock star insinuates himself into his teenage nephew's band -- that I'm inclined to go easy on it solely out of good will. It's likable enough, a lightweight rock 'n' roll comedy punctuated by several belly laughs -- but those laughs are all in response to the one-liners, and mostly from one minor character (more on that later). The story, the central personalities, and the uninspired slapstick are bland.
The title wannabe is Robert "Fish" Fishman, played by Rainn Wilson (of TV's The Office) in his first major film role. Fish was the drummer for Vesuvius, a mid-'80s heavy-metal band, but was kicked out on the eve of the group's success. Now, two decades later, Vesuvius is huge and Fish is a bitter has-been (or, rather, never-was).
He gets a new shot at glory, though, as drummer of A.D.D., an emo band whose keyboard player is Fish's chubby nephew Matt (Josh Gad). The lead singer and guitarist, sullen teen Curtis (Teddy Geiger), and bassist Amelia (Emma Stone) are reluctant, but Fish is actually really good on the kit, and he swears he can find them a gig.