Atlantic City's beaches are ok, but there are quite a few really nice ones a short drive away. All of the casinos are on the Boardwalk or within a block or two of the beach.
Water temperature should not be a problem, the Gulf Stream moves right up the coast.
One potential drawback... NJ just passed a smoking ban on all public establishments... except casinos, but only on the casino floor.
The law went into effect on April 1.
Smoking is not permitted in any public building (including bars and restaurants) and smokers have to be 25 feet from any doors or windows of such establishments.
This would include restaurants within the casinos. I am not sure if they stuck one slot machine along the side if that would qualify as part of the casino floor...
Hotels/motels can allocate no more than 20% of their rooms as smoking rooms.