Absolute minimum? Well for me, it's a game that works.
They may not be fancy, decorated by ribbons, and their battle might not be the best out there, but somehow, it just works.
Mapping : Functional
Optional : Functional, AND Pretty.
Remember, 'pretty' is just an option! A map doesn't have to be pretty, as long as it works! But of course, people would like to see a functional, and at the same time, pretty map. But also note that no one would want to see a pretty, but annoying map. I mean, it's a map that's pretty, but once you look at it, you go something like this :
"Wait, does this make sense?"
or something like
"Why can I something on this map? This is not right."
Characters : Well-Developed characters.
Optional : BADLY DEVELOPED CHARACTERS.
At least for me, a character that's good is one that is well-developed, balanced, blah blah. I mean, who would want to play/fight against a Mary Sue? No one, right?i would love to be a Mary Sue . Almost no one thinks that perfect characters are interesting. So, make your chars less-perfect. It might just work.
Maybe your character's able to control fire. Maybe they're able to control wind. Maybe even control other people. But what MOST people want to see is how they develop their abilities, how they progress through the story. They want to see how your characters react to situations, in the way that their eyes perceive it. Imagine if a little boy saw his mom getting killed in front of his eyes. I, certainly wouldn't like it if the boy just goes "eh whatever i'll forgive you" since it doesn't make sense! Unless of course he has quite the history with his mother. So like, by 'well-developed', I mean this:
"How did they get there?"
"What have they accomplished during that span of time?"
Story : Well-written, acceptable pace.
Optional : BAD STORY.
No one wants to play a game that has a horrendous story. Last time when I checked, someone had a status like "Tell me if you're going to kill my favorite characters, at least put a 'Game of Thrones' tag." Whether or not this was a joke, I think this quite well enough expresses the hate if your game has too many cliches. Or a bad-written story. Like, who wants to play a game where the main character was suuper weak. But after like, let's say, A DAY, they become horrendously strong just because?! okay that was probably not a good example but still.
A good story, for me, is :
A story that's not too fast, or too slow, meaning it has an acceptable pace.
A clear plot.
Good story structure.
edit: also i probably have no right to be saying this but who cares, i just did. hope this helsp