My reviewing system for films and shows that are NOT anime:
1-5: I hated it. I also don't think it has redeeming qualities, so you shouldn't watch it either.
6: I didn't like it. It's not my thing, I didn't like the execution, I don't want to see it again. However, I don't think it is a BAD film or show - it has qualities that will recommend it to those who like that kind of thing.
7: It was fine. I didn't love it, and I don't need to see it again. I won't be sad if I never see it again.
8: I liked it. I didn't love it, and while I'd like to see it again, I wouldn't want to see it often.
9: I loved it. I would be sad if I never saw it again. I might want to see it every few years.
10: I loved it beyond description. I wouldn't mind re-watching it every year.

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Clarifying my Anime rating system:
My number key below is an attempt to parse the small differences between 5 and 6, 7 and 8, & 9 and 10. When I rate, I consider my own enjoyment, the characterization and the plot, the appearance of the animation, and occasionally the soundtrack - in roughly that order. An anime will lose at least 1 point for presence of deal-breaker tropes (for example, comedic pedophilia), and more if the trope(s) ruined my enjoyment. On the other hand, it will gain at least 1 point for artistry in animation or sound. I don't expect to rate anything 1-4, as I would probably never finish watching something in this range of rating.

Cautious Recommending:
5: In this case, it started out with a higher score and slipped over time... because I normally don't watch anything that I would score below 6, except for movies (small time commitment).
6: I may or may not have watched the whole show, but I recognize deal-breaker issues in it, and I'm unlikely to rewatch. It just wasn't enjoyable enough for me to forgive its flaws. There would be huge caveats to any recommendation.

Likely to Recommend:
7: There's two types of 7s (ideally I could rank the second one 7.5). For the first, I didn't like it enough to think I would rewatch it, but also didn't see huge problems in the plot, characterizations, etc. and thought it was worth finishing. I might suggest it to someone if I know they like the specific sub-genre or other work by the studio. For the second, I recognize shows/movies that have high quality but just aren't my cup of tea. Not my thing, but usually I at least respect the work.
8: I had a good time watching it, but it didn't move me the way a 9 or a 10 does; it's possible that over time I would upgrade it if I liked it more on reflection. I would be willing to rewatch it if a friend wanted to watch it with me. I may or may not buy the DVDs (I'm more likely if there's something unique about it). I'd recommend it with the occasional caveat.

Highly Recommend:
9: I enjoyed it very much. It may have had one or two issues, but not enough to diminish enjoyment. It's possible that over time I would downgrade it to an 8 (changing tastes) or upgrade to a 10 (realize it's never left my mind). I'm likely to rewatch, and likely to buy the DVDs. I'd recommend it to most audiences.
10: Virtually flawless. I'd definitely rewatch, and definitely want to buy DVDs. I would shill this to anyone.

EDIT: for years when I'm participating in the MAL Anime Challenge, any anime in the Completed section with a * in the note was watched for the challenge. Similarly, if I'm participating in the MDL Drama Challenge, any drama with a * in the notes was watched for the challenge. Previous years' challenges will have their * removed.