Yesterday Jason finished playing a video game that had two possible endings. He chose one and was disappointed to find that his character woke up in an insane asylum, the whole experience having been a dream or hallucination. We got to discussing how this sort of ending often feels like a cop-out or lazy writing.
We also talked about it can sometimes be done well. In the case of The Wizard of Oz, for example, I don't know if it's because it's usually the first example of this kind of ending any given person is familiar with (given its classic family film status), or the fact that this was a new ending that audiences hadn't seen before - it doesn't feel trite. Discussing it, Jason also pointed out that Dorothy protests that it "wasn't a dream - it was a place," also kind of negating that "just a dream" idea by placing a question in the audience's mind.
I do like the stories that end with the character thinking or wondering if what just happened to them might be a dream or some other situation that didn't really happen - only to find that there is some object in the room, or something is different or changed in a way that can only be explained if the "dream" was real. I actually wrote a story like that once.
We had a competition when I was in 6th grade, and I won an honorable mention for my story. In it, my main character and her sister and parents were in a boat on the Amazon River. A tidal wave came racing up the river, capsizing the boat and separating the children from their parents. They proceeded through the rain forest having adventures and close calls, at one point, so narrowly escaping a snapping crocodile that the main character lost a piece of her shoelace. In the end, she wakes up in the boat, her sister and parents with her. She thinks it's all just a dream, until she looks down at her shoe and sees part of her shoelace is missing.