I got to experience Alien Encounter only once, when I was in my early twenties and I loved it. It was so scary and realistic. I really hate Stitch's Great Escape and I think I only went on it twice. The first one was such a let down after remembering how amazing Alien Encounter was. We tried riding it again several years later hoping maybe it was better than I remembered, plus it was indoors, short wait and air conditioned. But it was still bad, so we just skip it now.
I really wish my husband was able to experience Alien Encounter. He hadn't started visiting WDW when the ride was there. I understand that it's scary for young children, however, I think if people listen to the warning and use caution when taking their children. When I rode it, the line was an hour and a half long, vs. Stitch which is practically a walk on. It's better to have a ride where some of the people shouldn't ride because of fear levels, then a ride that most of the guests choose not to ride because it doesn't meet expectations.