For me it goes:
10 - Masterpiece: Not everything is necessarily perfect, but the flaws don't really detract from the show in any way. Anything in this category floored me in some way, whether it be visually, philosophically, etc. I try to make sure to keep things in the context of when they were created as well, because if something was a masterpiece when created and then defined a new genre, there are obviously going to be some shortcomings that are brought on by age, even if they weren't shortcomings at the time of creation.
9 - Excellent: These are shows that I really, really, really enjoyed. A lot. They made me laugh, or cry, or something, but—even if they left me wanting more—they had flaws that detracted a bit for me. Be it pacing, jokes that didn't translate well or fell flat, hard to ignore plot holes, etc. These are shows that I love, and maybe might be quicker to suggest than some 10s, but to me they didn't impress me to the same degree, even if they were a lot of fun.
8 - Very Good: These are shows that I enjoyed enough to consider them really solid animes, but I wouldn't be quite as quick to suggest them and they might have a pretty glaring flaw to them that I'm willing to mostly overlook because they are outweighed by the positives. Unlike 10s or 9s, these aren't shows that I finished and said "wow, that was amazing", they are shows that I said "yeah, that was a pretty fun show" and then mostly moved on.
7 - Good: These are shows that I liked enough that I was, at the very least, glad that I watched them after the fact. I wasn't impressed by them, but I did enjoy them and I might suggest them to someone.
6 - Fine: These are shows that had enough merit to them that I was okay with the fact that I watched them. I could have not watched them and not missed out on too much, but there was enough to these shows that they were still enjoyable. These are shows that are okay. I liked something about them, just not enough that I'd consider the show "good".
5 - Average: I could just as easily have not watched this show. Watching this show wasn't a mistake, nor am I especially glad that I did. It was just good enough for me to put up with it.
4 - Bad: I don't generally rate shows that I don't finish, so there aren't many shows that I'd give this rating to because I would have quit them well before that point. These are shows that I regret watching, but not strongly.
3 and lower - Very Bad/Horrible/Appalling: These are just greater and greater degrees of disdain. It's unlikely that I'd complete something lower than a 4, but possible.
Until the seven grade, there is no difference between our scales.