This is where the deceptively simple part comes in: to rock & to be rocked isn't really segregated simply to R&R & metal...within the past 60 years it has become a fleeting & repeatable state of being during a song that can be described as a human feeling, regardless of musical taste.
One can't really describe what it feels like to have been rocked, but if it were to be put into words, I think it would be that tune, or moment in a tune when you said to yourself: "Oh, F%$* Yeah!!"
& To further illustrate for clarity that being rocked ain't specifically relegated to just rock, I offer up a "Y'allternative" example of a rockin' moment just shy of minute 2: The Hangdogs- The Gun Song (you'll know it when you hear it)