4,5 to 5 = V.Good to Epic. It has that special "something".
4 = Good, fun to watch. I still have some good memories about those, and I like to return to few scenes.
3,5 = For me those don't have anything to come back to, although it was worth the time spent.
3 = Average, sometimes boring. Start of the drop zone.
below 3 = The drop zone. I value my time. Don't care about those. Not my thing. I won't rate dropouts.
Why then did I watch those time consuming series that I have rated at less than 3? I lost a bet. Few times. Fun times.
Ps. I'm really annoyed by high magic (power) settings, so my rating may be biased in that way.
Please note, that my taste may be waaay different than yours. I watch/read for fun, I hope you too.