(I've been to FOS once, never been to Revival BTW but hopefully one day)
FOS is indeed primarily about the hillclimb, but it includes wheeled (primarily motorized but not in all cases) vehicles of many many types, from the very earliest motorcars and motorcycles, to today's generation of F1 cars and running prototypes of street cars not yet released (for example, the test mule for the Tesla ran there in 2007 as did our very own PatrickO's 2 Eleven - the first customer car - several days after he took delivery). They say that typically about 1/3rd or so (IIRC) of the entrants are competing for best time in their class or overall (and therefore really hauling ass !!!), for the rest it's about the honor of presenting these historic cars at Goodwood and giving the crowds a chance to see them up close and personal - walking through the various paddock areas is probably the best part, though hearing and seeing the cars racing up the hill can be tremendous too. Rod Millen was thrilling, flying up the hill in one of his record-setting Pike's Peak cars... They also have constructed a rally stage in the forest at the top of the hill for the rally cars, and they have nonmotorized events that vary every year. In '07 there were professional cyclists (plus some guy named Damon Hill
) doing a hillclimb during the lunch hour, and in previous years there were gravity racers (sophisticated soapbox derby type vehicles constructed by manufacturers including Lotus, Bentley, Mazda etc.)
At Goodwood FOS, the invited entries can be of all sorts, whereas at Goodwood Revival, the types of cars are limited to the era during which the Goodwood racetrack was in operation as a competition course (1948 - 1966), to be in keeping with the "period-correct" style of the event. Many of the attendees and participants dress up in the style of these times.