My UPDATED Rating Scale:
Taking one of the bad ratings out to differentiate the good ones (especially my old 3.5 and 4 ranges) a bit more and moving the midline to 2.5
The Great: MUST HAVE MORE
5: One of my favorite series or seasons of anime ever -- I've only given out maybe 15 of these, and I gush whenever they come up in conversation.
4.5: Awesome, top-tier, best-in-season anime that I actively push others to watch. This is the sort of show or season that has aspects that are iconic, not just for this show or even just its genre, but for anime in general.
4.0: Beautiful, consistently engaging, very good anime. Beyond just entertainment, this is one of the best anime or seasons of its type, and I'd easily mention it in any discussion of the genre. There's a lot to like here, and I'd happily discuss it in detail.
The Good: Give Me More
3.5: Satisfyingly high-quality stuff. If something reaches this grade, every aspect is pretty solid IMO, and some aspects stand out significantly above average (art, plot, characters, etc.) This is good enough that I'd suggest it if someone were looking for recommendations in a particular category.
3.0: Solidly entertaining anime that sticks out slightly above the pile when considering that particular anime genre...but only slightly. There's nothing to write home about, and there might be some parts or aspects of it that just aren't good, but it's still a good show overall if you've got the time. I'd likely watch more of this without hesitation if it gets sequels or more seasons, and I'd certainly be happy to hear it got more, but I'm probably not recommending it to someone unless I know they're into this type of show. I only talk to people about this level of anime if I know they're already into it or if they're junkies like me.
The Meh: Don't Need More
2.5: Mid, with obvious flaws. There are weird plot points or characters that didn't really come into their own. While it's still watchable, I probably don't have much drive to watch it again or recommend it to others unless a later season is better. The type of show that makes me think "That was alright, but man I watch too much anime." (I see a lot of these.) I may watch it if it gets another season, but it didn't stand out enough to be excited about it.
2.0: I regret finishing this. Below average, disappointingly boring or incoherent...I probably waited for something to change but nothing did. Empty calories: not especially terrible, but not good. It didn't have much to say or do, it doesn't look good doing or saying it, and it's not worth the time. Possibly especially heavy on tropes, the characters didn't hook me, the plot fell apart or is just blah the whole time, or the whole thing's just woefully inconsistent. But regardless of why, I didn't enjoy it much and wouldn't watch it again. Unless I have reason to believe it'll be better in the future, I'm probably out.
The Ugly: No More, Please
1.5: I probably hate-watched this. For me to give something a score below a 2 means something was REALLY off. Maybe I disliked even the main character, their goals didn't resonate, or I don't even understand how their world works. Maybe I think the main character is a pretentious jerk and am annoyed that the rest of their world doesn't treat them as such...but I'm actively hostile about something in this show and will not be watching more.
1.0: "Worst of its type" shows with glaring flaws so bad that it can be used as exhibit #1 of its genre gone wrong. This doesn't mean everything is bad, but unignorable bad parts are ruining it for me.
0.5: I couldn't find anything redeeming about this trainwreck. It actively makes no sense, undermines its own mood-setting, doesn't develop its characters and villains well, and was a total waste of time from beginning to end. I only score things I finished, so that means I had some reason to think it'd improve...which probably means this is a terrible adaptation of something I actually liked in its previous format. Currently I've only given this to "The God of High School" anime.