I love first lines, but I don't use them to choose a book. I start with reviews if I don't know an author, then check it in the bookstore. The plot needs to interest me at least somewhat. And if I'm not sure, or if I happen across a book in the store that intrigues me either because of the cover or title, I then skim a bit inside, choosing a few pages at random somewhere midway through and see if the prose grabs me. I haven't been disappointed more than once or twice by a book since doing this, and I've read some wonderful books I might've passed on if I'd gone strictly by the first sentence and not a few halfway in.
First lines are not quite the first impression. That's the title, the author perhaps if the name is familiar, the cover design. The first line is more the entryway once you've gotten in the front door. Is it welcoming? Exciting? Interesting? Or is it a dump? I tend to assume most if not all first lines will be good. After all, they're the ones the author probably put the most thought into, revised the most, etc., especially if a new writer because he or she heard that the first line needs to be great. Never mind that the ones that follow better be good, too, in order for an editor to want to acquire it.
But because I love the first line game as much as anyone -- and I know I've posted this before, maybe on a message board -- here are some of my favs:
He drank alone. (entire first paragraph, John Steakley's Armor)
Harry cut through the morning rush-hour crowd like a shark fin through water. (Rain Fall by Barry Eisler)
Once you get past the overall irony of the situation, you realize that killing a guy in the middle of his own health club has a lot to reommend it. (entire first paragraph, Eisler's Hard Rain)
The gem-colored dream shattered, and left the kid gaping on the street. (Psion by Joan Vinge)
Someone was after me. (Catspaw by Joan Vinge)
Everybody has one thing they keep, one thing that matters to them more than anything else. (The Pickup Artist by Terry Bisson)
Jeff Winston ws on the phone with his wife when he died. (entire first paragraph, Replay by Ken Grimwood)
Isserley always drove straight past a hitch-hiker when she first saw him, to give herself time to size him up. (Michael Faber's Under the Skin)
The dead man's journey began above Honolulu, in one of the teashouses that orbit the city like hidden satellites. (Floating City by Pamela Ball)
There are a lot of others, but most were too long for me to want to type.
And I'll fess up. Except for a few where I recalled loving the first line, I was pulling books off the shelves almost at random. This is a game I could play all night and into tomorrow and have played it many times. Once, over the phone, my collaborator on the Mars books and I spent a couple of hours reading first lines to each other from our favorite books. And if we'd both read them, the last lines, too. Last lines can be as much fun to look at in such isolation. And of course, there's the classic Dahlgren by Samuel Delaney in which the first sentence is the continuation of the last sentence, making for a circular book. I don't have it anymore so I can't easily get the line to put here, but it was much talked about when it came out a few decades ago.
And what is really fascinating to me about this exercise is that many books I looked at, because the books themselves are memorable, the first lines were so-so or average, or good but have no real impact by themselves. It was the first page, first chapter, story, prose, the whole book that made an impact, all the pieces adding up to form something wonderful, and negating the first line needs to make the best impression theory. I think the first line shouldn't turn off a reader, and should be just good enough for the reader (ie editor) to want to read the second, and then the third. They're all building blocks, one leading to the next, forming a whole greater than any one part in isolation.