The new slogan is awesome! It's a refresh of the old So Big, So Fast, So Close, So Go commercials. You'll see signs that'll say Go Faster or Go Taller for Kingda Ka. Six Flags America's Facebook's info says something like Go Big, Go Close, Go Six Flags America, you're nations capital of FUN.
From SFMM's they have packets for all their events featuring Go Big stuff. One that really stands out is grad night.
Then it has the huge Go Big, Go Six Flags Magic Mountain logo. Tell me that's stupid.
Other way's to Go Six Flags are (for the kids) Go Looney, (for promo's) Go For less, and you can even Go Epic sometimes. That's all from the Grad Event. So personally, I love the Go Big slogan.
As for the new website, its great. Just a little to bright. But like GAcoaster said, it grabs you're attention, which is what they wanted.