Interstellar Pig by William Sleator
I read this book in third grade and it made a big impression; re-reading it today, I found it held up well. Interstellar Pig tells the story of a teenager on summer vacation who gets caught up in an intergalactic board game that proves to have dire consequences IT IS INTERESTING (don't even want to pause for a period in case I've already lost you) because the author spends the book playing around with subtle (and delicious) language mishaps on behalf of the alien characters. Also, the female alien is way hot, which even as a seven year old interested me strangely. If this is not enough, the imagery is tops: "A fat orange sun was sinking behind the island trees, and restless scribbles of gold danced over the dark water." But the best part is the way the teenager gets absorbed into the game while he plays it, not literally but mentally. We've all been there. (If it wasn't Doom, it was Super Mario 3 or D&D. Don't deny.)
I know the cover is queasy-making, but this is a good book to give to the kid in your life, or to your inner kid.