YA novels often have strong, compelling plots that adults will find enjoyable and very readable. The Hunger Games, The Fault in Our Stars, The Disreputable History of Frankie Landau-Banks, and Sherman Alexie's The Absolutely True Diary of a Part-Time Indian are YA novel I've enjoyed and urge you to check out. If you've read all of them, here is an additional list of titles from Kirkus Reviews.
Bonus Points: Data collected by the American Library Association show The Absolutely True Diary of a Part-Time Indian to be one of the most frequently challenged books of the 21st century. So if you read it you will not only enjoy a good book, you will strike a blow for intellectual freedom and get a jump start of Banned Book Week!
A good beach needs a good book.