It occurs to me that the opening sentence (or at least the opening paragraph) of a story needs to perform certain functions; it must be both an introduction to the story and a hook, both the greeting and the invitation to tea, and it should also set, to a certain extent, the tone of the story. The opening sentence is the rabbit hole, without which Alice would have never made it to the tea party, never met the red queen, and never battled the fierce Jabberwocky using her l33t hax0r sk1lz.
In some cases, the opening sentence transcends the mere requirements of it's function.
A screaming comes across the sky.
With these six words, Pynchon evokes an image that implies the entire trajectory of the novel. Is there any greater beauty?