Not really to anal about how I rate a series. I basically have four tiers for ratings based on how much I enjoyed the series:
10 - I really enjoyed it. Will absolutely rewatch/reread over again in the future.
9 - Had fun watching it, only tiny annoyances. Will probably rewatch/reread again in future.
8 - Not bad, couple of problems here and there. Maybe rewatch/reread if out of things to do.
7 - Meh, didn't really excite me to much but still managed to keep my interest. Most likely not rewatching/rereading.
Very rarely do I have usually have anything below those ratings since I tend to just drop the series and leave it unrated(I don't like rating a series I have not finished).
This is just a relaxing hobby of mine so I don't really see the point of forcing myself to finish something I'm not enjoying and then go whine about how terrible it was on the forums. Nor do I bash other people for liking a certain series, it's pointless.