Using only 5-10 for rating manga/anime (except when something really pisses me off by just how bad it is and I will give it 4).
The criteria is uhh, my enjoyment? Can be affected by the state of my mood. Objectivity does not exist.
5 = crap
6 = crap but I was feeling generous
7 = good but probably pretty forgettable and can't see myself rewatching
8 = very good but something is still missing
9 = damn, I LOVED this
10 = lifechanging and/or masterpiece