Hey there, just an anime watcher here.
My Personal Rating System:
1 star - Why. Why does this exist.
1.5 stars - Terrible, with very few (if any) redeeming qualities.
2 stars - More redeeming qualities than 1.5, but still bad.
2.5 stars - Almost unwatchable.
3 stars - Many flaws, but still somewhat watchable.
3.5 stars - Meh. Not terrible, but not super good either.
4 stars - Not the best, but pretty decent. May rewatch in the future.
4.5 stars - Very good. Almost perfect, except for a few flaws.
5 stars - Amazing. Can rewatch multiple times.
Note that not all the ratings I have on anime right now are totally accurate to my opinion. Usually I put them right after I've watched something, so my opinions sometimes change over time.