Berry brought together country music, blues, and the newly electric sound of the times in a mish-mash sound that is now synonymous with "rock n' roll." As the Rock N' Roll Hall of Fame put it, "it was his particular genius to graft country & western guitar licks onto a rhythm & blues chassis."
Let's take the song apart and see if we can hear just what they meant.
First, the rhythm & blues chassis. A chassis, by the way, is a word for the underlying mechanical structure of something (in this case, a song). R & B chassis shaped the song: the drums beat out a familiar 4/4 beat on bass and snare with the occasional cymbal. The driving bass line is pulled straight from the blues, running up and down a blues scale throughout the song with little variation. A guitar and piano are thrown on top—relatively typical for R & B of the era, but you might add horns or a saxophone over the guitar.
The guitar—Chuck's specialty—is where the real bending and melding happens. People have described Chuck's guitar riffs as imitating the piano and the horn section. You can almost hear a boogie-woogie piano part in the opening guitar measures. But that fast-paced strumming and twangy electric solo that is now immediately recognizable as rock n' roll was a new sound at the time. Country-western guitar players did it, but it hadn't been paired with the blues structure that formed the basis for "Johnny B. Goode."
The result is something that seems simple to us now. At the time, though, nobody even knew what to call it. Nonetheless, it was easy to listen to, easy to sing along to, and simple enough to imitate, even according to Berry himself: "Making it simple is another important factor that resulted in a lot of the other artists understanding and being able to play my music—if you can call it my music. But there is nothing new under the sun."