Kaido is very surface-level cool. Like, he looks cool and his attacks are cool. He’s cool if you’re a baby basically.
In terms of writing, he was an abomination and every single thing about him was wrong. I’ll bet not even Kaido’s most devoted fans can remember one single line of dialogue that this idiot said in 4 years of Wano. “Death completes a person” is the only Kaido quote that was actually somewhat interesting. I can give you my top 5 villainous Green Bull quotes right now but I’ll bet no Kaido fan can remember any interesting lines of dialogue from Kaido at all. “When you laugh, you smile!”
I did a huge post on this a while back but long story short:
Kaido is both a complete warmonger who wants to start the world’s greatest war, but also a complete sniveling coward too scared to let Big Mom enter his territory. Until three seconds later where he’s decided he wants to fight her personally.
Kaido doesn’t want Yamato to idolize Oden at all, to the point that he would physically abuse her for idolizing Oden. However, Kaido also refers to Yamato as his son, and the only reason Yamato identifies as his son is because she thinks she is Oden. So it’s like Oda forgot he was supposed to have Kaido hating Oden and now Kaido is referring to his daughter as his son? It’s like Oda forgot what he was even doing with this character.
Then you have characters like the Admirals whose powers all illustrate their characters on a symbolic level. Akainu’s magma fruit is supposed to illustrate his explosive personality, his hot headedness, it gives us insight into his “thorough justice” philosophy of eliminating evil without a trace, etc and you can do this with every Admiral, their fruits are symbolic to their actual characters. This also applies to people like Doflamingo who’s string string fruit showed him as both a manipulative puppeteer and also illustrated his secondary “spider” animal theme (all of the pre TS had primary and secondary animal themes to illustrate their hidden natures, etc).
And then you have Kaido. Whose dragon fruit illustrates…nothing. Because Kaido has no character. He is both a raging war monger and a sniveling coward, how are you supposed to give him a power that illustrates his character when he has no fucking character.
Kaido’s backstory was abysmal yes, but by the time we got to Kaido’s backstory I was just like “yeah, everything else about this character was awful and made no fucking sense, so why not”