The concept's actually kind of cute. A sweet schlemiel of a short-order cook working at a struggling diner (slogan: "It ain't great but it's food") stumbles on a new fashion in burgers and finds himself at the top of a fast-food empire, wondering--well, wondering the usual things likable characters in musicals wonder when they're suddenly wealthy beyond their dreams. That the authors of Burgertown trade in familiar tropes isn't the problem. That they've lifted a good many of them from recognizable sources--especially, and appropriately, Grease--isn't the problem. That they're unable to make good use of them is the problem. Ken Jones's book and direction stagger between parody and sincerity. Christine Jones's lyrics are weak. Jamey Strawn's music sounds like it was spliced together out of riffs from an old Casio keyboard. Endearing as the cast are, they can't overcome. Through 6/19: Thu-Fri 7 PM, Sat 2 and 7 PM, Sun 2 PM. Theatre Building Chicago, 1225 W. Belmont, 773-327-5252. $20-$22.