First of all, let's just say I'm a lover of all genres - be it wuxia, space operas, comedy, quick transmigration or yaoi, I've dabbled in them all. There are some I consider absolute masterpieces, and some I find utterly boring/ridiculous (though the author's and the translator's efforts should always be noted). Nonetheless, there are certain characteristics associated with the word 'quality' that I am partial to:

1, Logical. The novel needs not be completely realistic (it's a novel after all), but the plot and character design should be relatable to, if not closely mirroring real life people's actions and behaviors. For example, face-slapping is a popular element in many stories, but if a random heiress suddenly feels jealous and throws her whole life away to bully the MC, that's a no no.

2, Unique/original to a certain extent. Cliches can be utilized, but to an appropriate level only.

3, The MC is intelligent and reasonable (and composed - this one is my personal preference).

4, Let me just add this - readable translation, no MTL grammar-demolishing content.