It can be used to describe something:
* Positive: A fantastic adventure, a life-changing event, a truly amazing time.
* Negative: A very difficult or challenging experience, a traumatic event, something that was really awful.
The key is that the experience was strong and impactful, leaving a lasting impression on the person who had it.
Here are some examples:
* Positive: "My trip to the Amazon rainforest was one hell of an experience. I saw incredible wildlife and learned so much about the indigenous cultures."
* Negative: "Getting lost in the woods was one hell of an experience. I was scared and alone for hours."
The phrase is a bit exaggerated, but it emphasizes the intensity and memorability of the experience.