A Hook and a Promise

Don't you read at least the first paragraph before you decide on a book? The beginning of story lays down the promise for the rest of story and the author has to live by the rules she or he sets. I hate it when the opening of a book promises humor and delivers tragedy, or the opposite. I often chose my next read by my mood. Sometimes I want drama, sometimes light humor—whatever, the opening paragraphs guide my selection. If the book turns out to be something else, it's a disappointment. So, writers, be careful to open with the right tone. The beginning of your story should do at least three things: get your story going and set the tone; introduce and characterize the protagonist; and above all, engage the reader's interest!
The opening scene can also create mood, introduce the narrator or narrative voice, introduce other characters (one or two, possibly even three, but too many is just confusing and dilutes interest in the main characters), the setting, time, and so on.
For example, volcanic openings—those with high drama—promise that the rest of the story will leave you breathless too.  It's difficult to deliver on a promise like that.  Think about it. You may want to be a little more subtle in the opening, make a little less noise at the outset.  If it leads to melodrama later on, so be it.
Jennifer Crusie promises wit, romance, and a fun read in Fast Women.  It's all there in the opening, and she keeps it going until the very end.The man behind the cluttered desk looked like the devil, and Nell Dysart figured that was par for her course since she'd been going to hell for a year and a half anyway. Meeting Gabriel McKenna just meant she'd arrived.
Gwen Hunter opens Delayed Diagnosis with an ominous tone, and she delivered! I had never been a coward, but it took all the courage I ever had to walk in to Marisa's room. She was just sitting there, slightly slumped, her face and form in silhouette, framed by the window and rising sun. Unmoving. A mannequin in shadow.
I thought both of these books opened with a terrific hook and a promise. I'm sure you have examples of your own openings or other books with good openings. Share some! We all learn from seeing them.