The rail connection from PHL-ACY is not bad at all.
When you arrive at PHL, walk to the Center City Rail Line Station (inside the airport) closest to your arrival terminal. Take the train to Amtrak 30th Street Station (about 20 minutes). Once in the station (one of the largest in the U.S.) go to the information booth and ask where to get NJ Transit Trains to Atlantic City (there are 12 or 13 a day - see schedule below). The ACY train takes about 1.5 hours and ends at the Atlantic City Convention Center - about 3/4 mile from the Boardwalk. Free buses (I believe they are still free) meet every train and go to the Boardwalk and/or select casinos. Returning, the buses leave certain casinos about 30 minutes before every train departure time. Just make certain you check inside your casino for specific return locations and times. If you rent a car, your paying for a less than 70 mile one way drive of between 1.5 and 2.5 hours depending on Philadelphia commuter traffic. You'll likely not use your car at all in Atlantic City and may have to pay for parking it. There are many buses direct from Center City Philadelphia to Atlantic city - but that indeed would be a hassle for someone unfamiliar with the area.

http://www.njtransit.com/pdf/rail/r0090.pdf