We stayed at Artillery Ridge a few years ago and enjoyed it very much. Really cool with the horse corrals and stalls, and the "horse tours" are great.
You can do the audio car tour (CDs available everywhere, usually the various campgrounds will have them in the camp store) in one full day. It is a HUGE "battleground", encompasses the town and surrounding areas.
One thing to do that can be interesting is to find monuments from your own state, I think I remember reading that every state involved in the Civil War has at least one monument to fallen soldiers at Gettysburg. If you are really into the Civil War, detailed tours and reenactments are run regularly.