While there were a lot of characters (some of whom do come to grief, if you are a sensitive readers), I like how Josie and Eli are originally pushed together, but do eventually become friends. The last chapter address how people who lived through the nightmare are faring several months later, which was a nice touch.
It's hard to find scary ghost stories for middle grade readers, and Poblocki has a string of really awesome books. (The Ghost of Greylock, The Book of Bad Things) The House on Stone's Throw Island had a unique setting, threatening ghosts, and lots of pulse-pounding horror, especially in the water. If you were a fan of The Poseidon Adventure, definitely check this out!