Here is mine (for fiction):
1 star - truly terrible, little or no merits. not even so bad its good kind of bad. Will most likely drop the book. Whether we should even rate books we haven’t finished is another discussion. However, I am of the believe if a book has nothing going for it even though you’ve read 100 pages, it’s probably a 1 star.
2 star - it was ok. Enjoyed bits here and there. It did not feel like a waste of time, but would not read again.
3 star - this one is hard to define. it was better than ok, but not great. would probably not reread, but fairly enjoyed.
4 star - very enjoyable, would not mind rereading. maybe there were a few flaws here and there, but nothing detrimental.
5 star - this book made me think about it for days, weeks, maybe even months. I care about the characters like they’re my own family. I would want to reread it again and again. Although, there are some books I would not want to reread, maybe because it dealt with dark or violent topics, but I would still rate 5 star because of the impact it had on me. Did the book change me, did it make me want to reread it, those are pretty good criteria for me to see if the book deserves 5 stars.
Note, I have never really rated books until recently. I realize it helps me reflect on how I feel about the book, and helps me get closure and move on to the next book without any unnecessary lingering attachment. Unless its a 5 star of course, then I’ll think about it forever, haha. I don’t even have a goodreads or do reviews or any of that jazz, just thought it would be fun to discuss.
I use a weird grading system, but it is mostly for me. I don’t post my ratings anywhere outside of my reading journal.
A’s are books that are trying to say something serious and say it successfully (eg Brave New World) and it doesn’t matter how much i enjoy or don’t enjoy it as long as it made me think deeply about something.
B’s are for “i had a good ol’ time with this” regardless of literary merit (eg the night circus)
C’s are for “it was ok” (eg neverwhere)
D’s for anything I find myself thinking “i want my time back” about.
Some DNFs are Ds others are soft-DNF I mean to revisit later on, usually cause I think it has potential to be an A but I have to be on a different mindset.
I find this helps me think of literature and reading for fun in a more organized way. Cause Bs aren’t necessarily worse than As, they’re just different buckets. Sometimes I adore the classics I read and I rate them A+/B+ and sometimes i haaate a classic with a burning passion while also admitting that it was good at what it did and give it an A anyway.