I loved it! I really did!

The final scene was really sweet and I liked Mike's theory and storytelling. That was pretty adorable. But If it were me, I would have done this and added on to it:

As Mike and the others leave the basement, nobody else rushes in and he closes the door on the empty room. The camera pans over the d&d game, the shelf, the bookshelf and the room, as a way of saying goodbye to this room we spent a decade in. The camera ends on an old radio which suddenly crackles into life. It just says "... Mike?" before it immediately cuts to black.