Once upon a time, years upon years ago, a mother, who had absolutely no concept of manga and anime, purchased The Prince of Tennis Vol 1 as a lighthearted gift to put in her young tennis playing daughter's stocking. She was unaware that she would have to take slight responsibility for the being you are reading about today.
Rating series is really hard. I'm constantly going back and forth on how many stars to give. I've also been reading manga/watching anime for most of my life, so I'll often mark a series as completed but not give it a rating. This is mostly for my own personal checklist, and often for a series I read so long ago that it is difficult to remember well enough for an accurate rating. I'm in no way, shape, or form an expert. I have a lot to learn. I'm just a nerd.
However, if my opinion does matter at all to you, or you seem to find us having similar tastes, here is my best attempt at a scale:
5 - This series is dear to my heart. I've re-read it over and over again. It has reached a point where I am in denial about any faults it may (and probably does) have. (Or, it's just that dang good.)
4 - I really love this series. There is just one small reason (whatever it may be) that prevents me from giving it a full five stars.
3 - I like it. It is good. I enjoy reading it, however I wouldn't say I'm deeply passionate about it.
2 - I likely saw some sort of potential in it, there was something that made me press on and want to like it, but it ultimately dissappointed me.
1 - If I finished it, it was out of pure spite.
Also, if it seems that I am currently reading a lot of series at once, that is because those are the ones I consistently check for updates on. So, I'll keep them in my "reading" tab even if I'm caught up. I only mark a series as "stalled" if I consciously don't check on it for a few months to a year, OR if I am aware that it is on hiatus/a new volume won't be released for a while.