Garfield is a relative unknown, on his way up with parts in Never Let Me Go and The Social Network. He's an unexpected choice, namely because he's not on the public radar, but also because he's damn near thirty. Wasn't the whole point of the reboot supposed to be taking Spider-Man back to his younger days?
I'm sure the next big casting news will soon follow, for the love interest (will it be Gwen Stacy or Mary-Jane Watson?) and the big villain. I'm personally holding out hope that they add an adjective to the title, to further differentiate it from the Sam Raimi trilogy. The Amazing Spider-Man, perhaps?