Rattlesnakes are actually good creatures. They eat rodents. Yeah, total bummer if they happen to feel threatened and bite something they don't plan on eating (like your leg), but they are an important part of any ecosystem. I run into them regularly in my job (yes, we have rattlesnakes in Washington state), and they are usually more interested in getting away then using precious venom and energy biting a human. That looks like a big snake - if I see the pic correct - long rattle. Good thing he let you know he was there!