To rate something, 4 options are enough:
good, bad, mediocre and haven't watched yet.
Yet MAL gives us a rating system based on a scale from 1 to 10, so why not make effective use of it.
Objectivity/Subjectivity: I strongly believe that scores should be highly objective. What kind of shows we watch is depending on our taste and thus our selection is subjective in the first place. I believe our subjectivity is only worth 1 point, so if a show is trash but we enjoy it then we can give it a +1, sure that won't raise the rating to the top but atleast it will honestly represent our grounded opinion. Everything else should be based on objective truths and quality can't be dismissed because of 'muh feelings' or 'muh shit taste'.
I like to call 10 and 1 the subjective scores and reserve these scores for when I absolutely can't keep my subjectivity in check. Still I do not value them as fairly as the 2-9 scores.
My scoring system:
10 (Masterpiece) Nothing in the world is perfect, thus a 10/10 score is impossible and anyone who uses either 10 or 1 is highly subjective or a fool. Still there are shows that resonate with us deeply and even knowing that the shows are flawed, to us they are special and only then deserving of a 10 score.
9 (Great) The highest possible score a good show can get. These shows are not perfect but very close to it. These shows are so good that even without our subjective opinions they are still good. We can deny it but the truth is absolute.
8 (Very Good) These shows are good, really good. We enjoy every episode but after completing the shows and calming down, we retrospectively analyze them and recognize flaws, sometimes unforgivable flaws that stop us from giving it any higher score than it deserves. Still the show managed to show their full potential and the staff worked really well to produce these shows, they simply lacked in some departments to deserve a 9.
7 (Good) The shows are good and have something that puts them above the rest yet are still not good enough in some departments. Don't get me wrong, they are still highly enjoyable and can be favorites but to be honest they lack something. In some cases it is clear what they lack but most often it is not. One could ask what's the difference between a 7 and 8, the answer is not that simple. It all depends on the potential of the show and how well it was executed. If it succeeds it gets a 7, if it thrives after that then it gets an 8.
6 (Fine) These shows just barely managed to escape the average pitfall but still couldn't capitalize on their full potential. These shows did not try to be the the best and their lack of ambition can be felt. These shows are a one-trick-pony and only thanks to their gimmick managed to come this far. If they would have just put more effort then the shows would be truly good.
5 (Average) The worst score in my personal opinion. Shows can be good, they can be bad but if they are average then they are a failure. You can remember bad shows as how bad they were but average shows are simply forgotten. In a month or year, you won't remember what these shows were about. These shows struggled and fought so hard for 12-25 episodes and the most they can show for themselves is a mediocre 5? Truly a wasted potential.
4 (Bad) These shows are looking promising and are highly rated by cult fans but if simply take a closer look we realize that they are bad. They may start well, have a nice premise or a strong basis to build upon like original manga work but they completely wasted their potential by shooting themselves in the foot.
3 (Very Bad) The potential of these shows is thrown out the window along with the plot and common sense. These shows could have been good or atleast average but they did not even manage that. Just look at others and repeat like a monkey, is that too much to ask? How can you fail so miserably.
2 (Horrible) These shows are bad, bad in every aspect there is. These shows fail in art, music, writing and basic knowledge. The question is who made these shows, mentally disabled yet sentient garbage bins? These shows are highly overrated trash that any sane person would drop after the first few episodes.
1 (Appaling) As said in 10, this score is highly subjective and only haters and fools give it out freely. If something is bad give it any of the lower score as seen above, giving it a 1 only makes you look like a sour close-minded hateful fool. Still there are some shows that are so bad both objectively and subjectively that they deserve a complete 0 (abhorrent) but as we lack such a score, a 1 should do for these shows.