Britney is certainly a Pop icon.
BOMT and maybe Oops are iconic hits. Also, her meltdown was pretty crucial to 00s popular culture.
I wouldn't call her very influential, but a lot like Chris Brown in the sense that many artists identical to her popped up around her rise to fame, not because they were influenced by her, but because record labels were going with what they thought would work.
Also, she is the quintessential bubblegum Pop starlet - white girl with blonde hair, cute but with a sexy side, limited vocal talent, catchy Pop hits, etc.
