I've always wanted to visit Antietam.
Antietam is well worth seeing, and I hope you make it there sometime.
All of the battlefields mentioned in the article are worth going to, but some of the more out of the way sites left the deepest impression on me. The half dozen battlefields around the time of the Seven Days Before Richmond campaign are truly haunting, not only the large ones, like Malvern Hill, but especially the smaller ones like Gain's Mill and Bever Dam Creek.
Antietam is deeply moving. Especially on an early-fall day. The most amazing and moving sight is the annual Illumination, in which volunteers light a candle for each of the soldiers killed at Sharpsburg, and set it out on the field. You don't realize what a horror it was until you see those candles in their thousands, spreading out across the hillsides, each one the symbol of a single flickering soul.
I almost got to Gettysburg a few years ago when my I was visiting my brother (who lived in PA at the time), but the one day I could go was raining and very cold, so I didn't get out there.
Well, he lives in Maryland now, and while I'm up visiting in August, he and I and my nephew are going to go camping for a few days in the mountains up there, and we're going to take in Gettysburg and Antietam. I'm really looking forward to it.