I don't hate Mutant Mayhem or think it's the worst thing ever(I'm actually someone who likes MM April and gets annoyed when people are racist and/or fatphobic about her!), however I have one major gripe with it:
The way that, at the end of the MM Movie, the Turtles are outed as mutants, and then accepted as public heroes and allowed to go to human school with April!
Some of this is my bias, because I'm a former homeschooler and the TMNT were some of the only popular characters I could relate to in that way, and they just went and took that away from me in the new movie
But also, even without that, it is literally a core theme of TMNT that the Turtles are outcasts and shunned by society, but they save people regardless, and they love themselves in spite of that and find people who really care about them! And that theme is completely taken away by having them be popular public heroes and accepted enough by society to go to school like humans!
So I just can't like it, and it's not just because it's The New Iteration(even if i am pissed that MM being made essentially killed off any hope of saving Rise)