A note about my rating system: I don't use low votes for a reason.
I personally believe that most fiction stories have some kind of value and given my experience with the Italian grade system (if you take under 4, you REALLY tried hard to get that 3/2), I prefer to use mostly the grades between 5 and 10 while saving the 1-4 for truly horrible things that deserve shaming.
In addiction, I think that objectivity can be reached in reviews, but it's hard and still not 100% accurate: because of this all of my votes are to be seen as "X +1 or -1", considering my personal bias.
In addition to this, I am a fan of japanese fiction, but I mostly read novels and manga, so It's rare for me to watch an anime when I think that they are gonna be worthy of incredibly low votes
1) Absolute shit, beyond any kind of saving.
Personally, to give 1 I need to not even be able to appreciate this shit ironically.
As of now, I haven't seen any anime worthy of such a low vote. I hope I never see them.
2) Awfully bad on all levels, but at least one element was decent or I was capable of enjoying while making fun of it. There is something you remember, surrounded by the rest of the trash it is.
Example = "King's Game The Animation" which doesn't get a 1 only because some scenes were fun to watch with a "Absolutely bad slasher teen horror" POV.
3) Seriously bad, heavily flawed.
Some parts of it were ok, but most of it was just too bad for me to enjoy it even a little. This is where if you like a specific genre things can be a bit better but I still absolutely suggest you to skip this shit.
Examle = SAO in Alfheim Online
Bad and still not recommended to anyone, but there was something at the core that could have been decent. The difference with 3 is that the problems aren't as heavy as before and many people will probably enjoy it. Not me.
Example = First half of SAO. I actually digged the concept in the first episodes (not having read the novel back in 2012) but it doesn't take much time to turn into the reason people use Kirito as an insult.
Not too bad, not too good. It has decent elements, but also something bad.
It is not memorable and I wouldn't suggest it to anyone.
Example = Fate/Stay Night (Fate route) 2006.
I am a fan of FSN, like, really a big fan, but this anime is a bad adaptation. If you like the concept of the series, you will probably like it, but you will also miss most of the really good things the novel has. So I wouldn't suggest it, but it's not trash.
Good ratings starts truly here.
Overall, a good anime/manga, enjoyable but with problems that could ruin the experience. The good parts are more than the negative ones, and in general the negative ones aren't that heavy or they don't directly reduce the effect of the good ones.
Example = How to summon a Demon Lord. I liked this anime, but it's nothing that I would suggest to many people. The ecchi is good, but the actions scenes were mostly "meh". I like the characters tho, so In really I would give a 6.5 here.
This is where the things I truly likes begin, with good elements in most areas.
Problems aren't that much relevant and the rules for good writing are present (conflict, chara growth, empathy, good usage of tropes of the genre, likeable cast, stakes, originality...).
Also, even with problems, a series can be this good with a good writing for its strengths.
Example = Attack on Titan. You see, I am actually a big fan of the manga, but the anime wasn't the best. Yet, its strengths are enough to make me appreciate it more than other things with serious flaws.
8) Very Good.
Just as "7", but buffed.
The good-writing elements are really well used, with few errors that interact with the good ones. Yet, something could have been done better. In general, a "8" is a totally solid series that I seriously encourage people to see (at least, if the genre isn't your kryptonite. I just can't stand series about cute girls doing cute stuff and only that).
Example = Overlord. As opposed to "How to summon a Demon Lord" that got a 6, Overlord gets a 8. The characters are way more original and entertaining just like the concept, the MC is even more funny and likeable and while some ecchi/fanservice-y elements are present they do not ruin the mood of the series as a whole. The action scenes are also pretty good, while not stellar.
Top tier anime, must seem
With strong points in all relevant parts (maybe, not too original, but that's not needed to write a Great fiction if you are skilled).
Everything, or almost everything, is where it should be. The problems are so few or so small that they don't touch in any way the general quality.
It just works.
Example = Asobi Asobase. THAT'S how you do comedy with a touch of nonsense, not like many other anime.
Example = MyHeroAca. This is what I expect from a new generation shounen that can challenge Naruto in popularity, and that can even challenge One Piece for the place in my hearth as "my favourite shounen anime"
10) My favourites.
I don't like to shout the word "masterpiece" in these days like many others.
10, for me, it's just like 9, but with something more that hits my personal tastes.
10 is something that I think that is on the same level of the 9 -objectively speaking- but I just can't stop myself from giving something more.
Monogatari Series is a 10 because I just love Araragi too much, since I strongly feels something in his character that reminds me of myself and my personal life. The characters are well written (but this is due to the original writer, a freakin genius) and the VAs are top-notch, the music tell even more than the words at times and the animation is just too beautiful, as the scenary itself.
Howl's Moving Castle is just too beautiful. Can't say anything else. Every single time I watch, I love it more than before.
Baccano is something that I watched only lately, but I still gave it 10. It may not be the most easy series to get into, but damn, it is a masterpiece of storytelling.
It really, really, really uses the rules of modern writing very well. And seeing an anime doing it, it's even better!
The original novel is cool, but somehow I liked the anime even more, thanks to the OST and really good VAs