They did virtually everything first, in popular music, for nearly a decade. The rest of the prodigious talent in the music world of that era followed them. They crossed the line from a blend of pop and rock all the way to avant garde and back again. They innovated, pushed the envelope, even at times to the point of atonal irritation (Revolution #9), at other times managed to make the weird and atonal just lovely (Strawberry Fields), and they pulled it off; they made us love it. They ushered in an era in which the best popular art was also the most popular art, and the impact of that even went beyond music. In the 70s, in the wake of The Beatles, the radio played progressive, genre-bending stuff. Bands like Zep and Spirit and Tull and King Crimson found big audiences. Imagine that happening today. The Beatles made that possible. What's more their massive influence on popular culture spilled over into other art forms. Think about some of the movies that were blockbusters in the 70s -- It was the equivalent of a Darren Aronofsky film festival at the multiplex.
Of course they didn't do all of that alone, but if hadn't been for them, I'm not sure it could have been done. They weren't just a band, they were the catalyst of a cultural revolution. You can dislike them, but if you think they're not important you're just not paying attention.
Tim