Spectacular. Given the understanding of the Flash CS3 layout, this is definitely a pretty solid piece of background art you've got here. It's very captivating, and the coloring is spot on. It almost gives me a bit of an Adam Phillips feel, which is especially impressive. What caught my eye first- aside from the lighthouse of course- was the detail and rigid outline of the leaves on the trees and their respective silhouette. Honestly the only thing that sticks out to me is the amount of blur given to the clouds. I'm assuming since this is background art, the clouds are probably meant to be in motion. Considering this I'd recommend maybe bumping the blur down a few points- only a few. Regardless this is a great piece you've got here.
I have to ask- is this any particular lighthouse you referenced, or one you drew up on your own? You've painted my dream home.