It's very seldom that a sunset or seascape comes across this violent. When you get to know the poem (and very real history) behind it, you get it though.
Turner cleverly goes to work by grabbing your attention with a stunning sunset and then shifting your focus to the slaves that were pushed overboard for an insurance claim. The hazy, scratched brushwork conveys perfectly the panic and confusion that must have been felt. I think the right description would be 'hauntingly beautiful'?
Not a funny one, I know, but it would have been an injustice to just say "pretty sunset".