I didn't knew SMS was hated that much by MB until i saw these posts
But most what people said here is the truth
SMS is so overpowered, and has little to no weaknesses, that takes out the entire challenge/fun of the game out.
About the design of the character itself, I'm kinda mixed about it
I Don't mind much the shading of the sprites, but the sprites really are just flashy and too bright, and SMS is basicly and OC from someone that mixed Sonic Or Shadow, and decided to make a SRB2 Wad Character without any kind of interesting backstory or any fun gimmick to make the character good, besides from being horrificly fast.
When you make an character, or either play as one, what makes it fun is not only it's strenghts, but also their weaknesses, like Sonic, He's really fast, and his Thok can help him to reach further distances/jumps, but his biggest drawback, is that he can't really reach high places without the help of springs, badnik jumps or characters to help him like Tails.
Or Knuckles, which his glide and climbing abilities gives him more possibilities to go at higher and hidden places, as also his ability to break rocks without the need of spin dashing, but his biggest draw is that he can't really jump that high and reach high places without the help of his climbing ability or even its glide to avoid pits and falling to death, unlike the other characters.
You see what makes playing with these characters interesting?
It's using their strenghts to overcome their weaknesses, and all of them have something unique into them, making them different from each other.
SMS in other hand
Is awfully unbalanced.
SMS has little to no weaknesses or any kind of unique traits at him (Except by the OVERPOWERED QUALITIES) that makes him unique among all these characters.
The fact he has no drawbacks, it takes all the fun or challenge that the game could offer you, he runs fast, his spindash charges in no seconds at all, his ghost thok let him reach higher places (Even more than Tails fly ability) and you can use it about almost anywhere and there's really no limit on how much you can use it, then, making the entire game really easy with no challenge at all
a Character like him should have a drawback like:
Starts with 50 Rings, loses 1 each second, when reaches 0 dies instead of de-transforming, Thok uses 2 rings at each use, can't turn into super, instead tokens give you 25 rings each one you collect, and every time he gets hit he loses 5 rings, his ghost thok uses 10 rings at each use, everytime you kill an enemy you get 2 rings and if you use and uncharged spindash, you consume 5 rings.
If SMS wasn't really SMS, maybe it would be a better character, it's only a faster Sonic Reskin with shadow aspects, it's trying it's hardest to be edgy and cool
But in the end it's just lame overpowered character
I don't think we really need SMS anymore, or at least until it really gets good
By the time of 1.09.4 this kind of quality was fine
But at 2.1 or 2.2
No way, we have lots of interesting wads like Dirk The Husky, Jetsyn and even Shadow Or Silver that takes advantage of the Lua scripting to make interesting things to their gameplay.
SMS won't be missed tbh, or at least until he makes something worth to be at MB again.
TL;DR
SMS is only a faster Sonic reskin with shadow fused in, and lacks and removes any kind of challenge or fun at the game, Unnecessarily overpowered and tries too hard to be cool and edgy.