I want to take them on and emotional, roller coaster journey of two people falling in love - the good bits, the bad bits, and everything in between. I want them cheering on my couple the whole time to make it to the finish line together, and then I give them the well-deserved happy ending that makes the whole trip worth it.
It depends, really. But mostly, I want to elicit a clear image(s), build an emotional response from them (exact response subject to change with the type of writing and genre), and give them desire to read more.
My goal is to educate readers about the incoming Rapture, but also to entertain with a great story that peaks their interest in the subject.
I write romance, so I want them to feel the way they felt with their first love. I want their heart to race, I want them to swoon because that's what I want when I read books. I want it to feel like the first time you ever held someone else's hand or the first real kiss when it was good. I want my readers to lie awake at night, wondering if there are really people like my character's who exist and who really are that in love.