Antietam was a very different experience for us than Gettysburg. As you probably know, Gettysburg is more "popular". The result of that popularity is a glaze of commercialization that sits over the whole experience (at least for us it did).
The commercialization was absent at Antietam and in it's place was a feeling so intense that it took me by surprise. First a little background for you:
"The Bloodiest One Day Battle in American History23,000 soldiers were killed, wounded or missing after twelve hours of savage combat on September 17, 1862. The Battle of Antietam ended the Confederate Army of Northern Virginia's first invasion into the North and led to Abraham Lincoln's issuance of the preliminary Emancipation Proclamation."
(from the NPS website)
...the bloodiest one day battle in American history.
You could FEEL it. I don't know how to describe it, but there was just a very heavy feeling there. A very sad feeling. I wasn't expecting to feel that way (Gettysburg didn't feel like that), I seriously had to struggle not to cry as we walked around. And I rarely cry, so that should tell you how intense it was.
After walking around outside, we went back into the visitor center to check out the small museum and watch the film. I recommend both, but with a word of caution for younger children. The film was a bit graphic---when the kids were finishing up their Jr. Ranger books with the Park Ranger, he asked them what they thought of this or that...he asked my youngest what he thought of the film...Tristan replied, "I thought that it was inappropriate for children."---(Ha! out of the mouths of babes...)
**A couple of pages from the NPS website that give first hand accounts of that hellacious day... here and here. I warn you, though, they are very hard to read...