William Finn and James Lapine's musical is tricky. The protagonist--sexually ambivalent Marvin--is an immature kvetch trying to hold together an extended family that includes his ex-wife, their precocious son, the ex-wife's husband (who's also Marvin's shrink), and Marvin's boyfriend, who suffers from a mysterious malady we know is AIDS. (The story is set in New York circa 1981.) The situation is soap operatic, the neurotic characters are irritating--unless the cast can achieve an emotionally nuanced balance of pain and humor. Steve Scott's staging for Porchlight Music Theatre Chicago merely scratches the surface. Eugene Dizon's musical direction is up to the standard of Finn's ravishing ballads and complex ensemble numbers. But the fine singing isn't matched by sensitive acting, except in the case of Holly Stauder, who brings depth and honesty to the ex-wife, a woman confused by the way her life has defied conventional expectations. Through 4/16: schedule follows. 3/31-4/2: Thu-Fri 8 PM, Sat 2 PM. 4/9-4/10: Sat 8 PM, Sun 2 and 7 PM. 4/14-4/16: Thu-Fri 8 PM, Sat 2 PM. Theatre Building Chicago, 1225 W. Belmont, 773-327-5252. $27-$30; $95 for a festival pass to all four shows.