I love the promise of first lines in a book.
It isn't that I'll stop reading at the first line, but if it's amazing I find I'll put more effort into the reading. I love the questions they provoke and the tone they set. Here are a few that make me want to read on:
"A mountain range of rubble in which our narrator introduces: himself--the colors--and the book thief"
"The air crackled like a gathering thunderstorm the moment the girl entered the chamber."
"The Austrian horses glinted in the moonlight, their riders standing tall in the saddle, swords raised."
"I had arrived early for my own assassination."
(Jennifer A. Nielsen)
"There is one mirror in my house."
"The screw through Cinder's ankle had rusted, the engraved cross marks worn to a mangled circle."
"A tree branch slapped John Craig across the face, scraping his skin, but he kept on running and ignored the stabbing pine needles on his bare feet."