COUNTRY/BLUES. Bonnie Raitt - Longing in Their Hearts (Capitol):. Bonnie Raitt's ``Longing in Their Hearts'' may elicit more longing in the hearts of her die-hard fans for that snappy, rollicking * & B style that's so resonant in her Grammy Award-winning ``Nick of Time'' (1989) and ``Luck of the Draw'' (1991). Except for an upbeat opener, ``Love Sneakin' Up on You,'' and a few irrepressible country-bluesy tunes, the singer-guitarist's latest album downshifts toward darkness. Yet its melancholy tone jibes well with emotional lyrics to reveal an even more thoughtful Raitt. The title track, co-written with her husband, actor Michael O'Keefe, uncovers Raitt's theme: longing for a higher level of happiness than is reached through material success.