Not as good as I was hoping.
First, the Camelbak valve is really cool. You should buy a Camelbak bottle just for that. And the "Big" in "Big Chill" is important, because being able to carry 25 ounces is awesome. I go through that in 20 miles. But it doesn't keep stuff THAT cold. It certainly doesn't keep stuff cold for hours, but it does keep it colder than if it was in the sun. It's not bad, just don't expect COLD.