Dark throughout most of the ride. You see scenes with skeletons, alligators, alot of the Queen/witch. Loud noises. This is the one in DL which I don't know if it differs much from the one in WDW. Should be the same I would think. The one in DL is actually called Snow White's Scary Adventure. (Maybe someone can confirm if the two are the same in both places.)
My kids were never scared to go on it but they were unusual in that we had AP's to DL, and they grew up going on these rides as opposed to hitting it for the first time at age 3-5. Try it once. See how it goes.
Oh, and one more word of advice. This can be applied to alot of situations not just the rides. I've heard alot of parents say to their kids right before they go on "Don't be scared. It's dark with a scary witch but it's all pretend and mommy's right here." Right. That'll work. If the kid wasn't scared before they will be now! I just always said how much fun it was going to be. Don't make a big deal about it before hand. If they ask just be vague and repeat how fun it will be. Most of the time the kids don't know to be scared until their parents tell them they might be. Just my observations.