I don't really "plan to watch" anime, because I want to see pretty much everything.
On the other hand, I "plan to read" manga, because I only want to read really good comics. (That is a lie.)
My anime scoring system is expressed in words below. Although I'm not entirely consistent in using them.
[10/10] Perfect: Works of this class combines a great audio-visual presentation with a masterfully told story, but most importantly it appeals directly to my personal senses and feelings. It may not be "objectively perfect", but nothing is. No, it is merely perfect for me, a work with which I have no objections whatsoever. This is anime that I often think about.
[9/10] Fantastic: An anime that stands head and shoulders above others. Perhaps it's expertly crafted all around, or there is some single aspect (like story, style, or just pure entertainment) that makes it truly excel as a work of popular culture.
[8/10] Very Good: In terms of writing and production, these works maintain a high level throughout. Whether it is insanely comical, adrenalizingly adventurous, chillingly suspenseful or heartbreakingly emotional or something else, it's effective.
[7/10] Good: Perhaps it was a show that was lacking in production but made up with likable characters and an interesting plot, or it had good production values but didn't use them properly. Possibly it was good, but just not good enough to warrant a higher score.
[6/10] Okay: It's lacking in some aspects, but has some good points that makes it a fun watch. It could be some interesting artistic turns or some fulfilling content, or just be the right amount of "kitsch".
[5/10] Mediocre: Not good, but not awful. Perhaps it was mundanely produced, or it had non-imaginative writing, but it's not without redeeming qualities either. Could have gone without watching, but I don't regret it either.
[4/10] Bad: It could have been okay, if one or two aspects were changed. Perhaps there are extremely annoying and unlikable main characters, a disgusting art style, a mind numbingly boring or stupid plot or it's just a work done without any real finesse.
[3/10] Very Bad: Instead of just one or two flaws, anime of this class really hasn't got anything good going for it. It either holds a thoroughly very bad average level, or there is a black hole of suck in a sea of mediocrity.
[2/10] Awful: Works like these cannot be made by people merely without talent. It takes something special to be this bad. It's so offensively bad it blows the mind.
[1/10] Atrocious: It's so bad that you're actually a worse person just for having seen it.