I've read first paragraphs that were long--too long, and some that were only one sentence, but even in those shorter ones there are promises of tone, character, motivation, conflict, that ideally prepares me for what is to come. I wish this were always the case, but it's certainly a good reminder for aspiring authors (notice how I didn't say aspiring writer).
If I'm drawn to a book by its cover, I'll give the first paragraph a read to see what I'm in for. If I want to read paragraph two, I'm in. That being said I've DNF'd books 200 pages in from authors I loved. When this happens I'm so disappointed. I question myself, wondering if I'm dumber than everyone else who loved this book. Maybe I am. But the truth is, the rest of the story, the "follow through" from that opening paragraph, just isn't doing it for me.
Loyalty to an author I've previously enjoyed will induce me to start the novel, but no loyalty will force me to finish it if isn't delivering on the opening promises. It sounds harsh, I know, but I just don't have the time to be bored or frustrated. Feelings none of us want our own readers to experience. This doesn't mean you need to answer every question or deliver on every promise. But that opening, that great hook you wrote, should not be in isolation from the rest of your story, but a lead in to your story and the world of your character.