Kevin Hearne (Iron Druid) is really good at this, with his growing number of novellas adding to the main story, a side quest, or an explanation about why a character is a certain way or how they came to know what they know. I have enjoyed all of the short stories and novellas in the Iron Druid series and am definitely up for more!
In general for me, if I have that back story and character knowledge already in my head, then I'm happy to read a short. If not, I may read it, and it may be fine, but it probably won't stick with me, unless the idea is just really compelling. I'd like to highlight Cascade Point by Timothy Zahn (a Hugo winner from 1984) as an example of that. Unfortunately I'm not seeing a readily available version of it as an e-book, mostly just used paper copies on Amazon, so you might be able to find it that way if it sounds interesting to you. I'm wishing I still had my copy so my husband could read it. I was surprised he hadn't already because he's more the Sci-Fi Guy and I'm more the Fantasy Girl, but in this case I was ahead of him! ;)
Cascade Point struck me as such an interesting idea, and what really made me think was when the navigator in the story would see his reflections stretching away, in different uniforms, one as an admiral and he wonders what that parallel self did to become that, then he watches it move away from him down the line of reflections over the years. It just really struck me as a fantastic visual for what many people go through in their lives, wondering what they might have done differently and how that would have played out. Would it hold up if I read it again? Hard to say, but at the time it was something new and different to me and really grabbed my attention, sticking with me ever since.
Maybe I just need to read more from the Hugo's list! I would love to hear more suggestions on short stories or novellas that have really stuck with you, especially those that are stand-a-lones, not part of a series.
Thanks again for dropping by!