First: I think this is work of good amateur. A good amateur who know how to make a lovable main character despite lacking skill to make an outstanding story.

The best thing about this novel is the main character.
She's an absolute cute awkward introvert who's lacking common sense about social skill which make her an adorable character. Her thought, action, and sometimes unexpected quotes is the one make me love this novel.
She got OP power but her personality isn't like those usual heroic isekai protag.
The second likeable character is the MC's only friend. His personality is more shown than the rest of the characters. But not good enough because we can see that his only purpose is to be the MC's friend.

On the other side, the story is the one I find lacking.
The good thing is: this story didn't copy all the "RPG bundle pack template" like Adventure Guild Class system etc. Only medieval, magic, level, and demon lord. Still templateish but at moderate level.
The plot is so rushed that it only capture the main events, skip few monts, main event, and so. The author skipped most the "micro development events" which where we the reader can get absorbed by the character.
The plot fail to 'catch' the reader to love the characters from simple daily encounters. While those small events are the one that make us see all the colors of the characters. Instead the plot is rushed which is not eventful as the plot is so linear already.
The plot is so brief that it look like a rough draft of a better novel.