My rating system:

10- Perfection. Even god binge-watched and loved it.

9.5- Near perfect. Some things could be changed, but none that I remember a few months after I finish watching. Mostly 0.5 was deducted for the fact that it got over. Was sad that the joy of watching it for the first time is now gone and I most likely suffered a hangover and/ or rewatched it as soon as I finished watching the first time.

9- Really damn good. But if I could, I would change a few things. These things are significant and made me think about how the drama could be better if they were done differently. Mostly made me write alternate endings that are a bit closer to my vision for the show. But would give a rave review if anyone asked.

8.5- Very much enjoyable. But lacks the oomph to be classified as a 9. drama.  Maybe found it overhyped, or underwhelming (due to my expectations/ reviews). Someone else could rate it a 10.

8- Better than average. Really enjoyable. Would recommend. A solid drama. Made me happy that I watched it.

7.5- Maybe I wasn't the target audience for this show and could've done without watching, but still had fun so not a total loss. Maybe it started out good but fizzled. Some scenes are memorable and I would rewatch them.

7- Meh. Enjoyed, it but couldn't wait for it to get over. A couple of terrible things, but the pros outweigh the cons. No hard feelings as some shows are like this. Average. You simply move on.

6.5- Good god, no. I definitely did not have a fun time watching, but for whatever reason continued. Wouldn't rewatch it. The cons outweigh the pros by a long shot. 

6- Worst than good god, no. Did not even have fun hate-watching it.  Would not recommend it. Refund my time level bad. Would warn others not to watch.

Anything lower than 6 is really bad imo. Even if I didn't hate watching it, did not like significant things relating to the plot, script, writing, direction, acting, characters, message, and/or pace.  I probably hated myself for watching and the showmakers for making the drama. If I could, would try to delete this drama from dramaland.