One NME (New Musical Express) reviewer wrote of Britney's music:
Like it or not, the songs penned for Britney by Swedish producer Max Martin, the man behind the even more successful Backstreet Boys, get into your brain like ketamine. An all-encompassing, horrendously realised high—once it's inside you, there's little you can do to stop it, you must give in. In its own sick way, Britney is drug music. (Source)
NME might be exaggerating their claims a little bit, but the point is valid enough: the greatest pop songs make you feel good, and "...Baby One More Time," even though it's essentially about loneliness and lost love, is a feel-good song. The song is built on a minor chord progression in C Minor, and launches with a memorable three-note riff on a low piano octave. For a dance song, its elements are surprisingly rock and roll: the main musical components are drums, the booming piano, a wah-wah guitar part, and a mechanical bass line. It could almost be rock if its main feature wasn't Spears' sugary, famously over-modified vocals. The final effect is a memorably fun song that might not be drugs, but is definitely candy.