From its plain brown wrapper to the goodies inside, the latest Zep album is full of surprises. Added to the predictable (and welcome) hard-driving, thunderous guitar numbers are some touches of reggae, a little C&W and, lo and behold, a couple of ballads from Robert Plant. Guitarist Jimmy Page pounds home the usual Zep message on In the Evening, and another cut, Carouselambra, though intricate and mysterious, has a familiar ring. But there's also the surprisingly plaintive All My Love, the twangy after-hours-on-the-highway Hot Dog and a spicy Caribbean number called South Bend Suarez. If the boys have been away for a while (this is their first new LP since 1976), they've obviously had their ears glued to the radio. The result is an astonishingly eclectic, satisfying LP.