To be honest, I don't really use MAL as my main website anymore (that would be anilist). I only come here to read reviews on stuff that I'm not sure about lol (and sometimes, when I'm inspired enough, I also write some reviews).
The rest of the time, this gets updated through my kitsu account. But either way: you can still get a pretty good image of me just by looking at my lists.
I rate based on enjoyment, sometimes I take the rest into consideration, but most of it's pretty much "hmmm how much did I like this?". My rating system goes like this:
10 - perfect (to me). is it flawless? proooooobably not lol but I don't care, I loved it so much
9 - excellent!! There's probably a thing or two that could've been improved, but it was still amazing enough
8 - LOVED it. It's not "as good" as a 9 or a 10, but it's still pretty good and I had a good time watching/reading it.
7 - had some good parts but could be better. Not very good nor very bad, to me it's pretty much in the middle.
6 - meh. didn't like it, but didn't hate it either. lukewarm at best.
5 - didn't like it but not to the point of hating it
4 - disliked it. very much. if it gets rated from 4 to below, it's all downhill from it.
3 - HATED IT but there's two or more redeeming qualities. Or even: I'm too much of a softie to give it an even lower score (for whatever reason).
2 - HATED IT but there's at least one redeeming quality
1 - ABSOLUTELY HATED IT and there are no redeeming qualities about it
Every now and then I might change the score of something but this system is pretty much solid to me. It might get harsh sometimes but, well, that's just how it is.