These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Thirty Sue Pileup: Let's see... considering that the heroes are immediately accepted in the other worlds despite changing things up immensely, and never actually fail, they are probably two Sues, who are constantly attacked by a Villain Sue who turns out to be an alternate version of the protagonist who gave in to his base desires.
Word of God confirms this is the case. The Token Loli groups chosen (and by extension the whole chapters) are based on his favorites. He got a bunch of fantasy-fulfillment plots and mixed them with some What If scenarios that seemed interesting.
Most of the series are rather obscure /not mainstream enough.
Word of God informs us that the most visited chapters are, and I am not quoting the Bible: 'the First and the Last'. What does that mean? If you skip chapters because you don't like / don't know about the base series it uses, of course the ending will take you by surprise.
Mike is not a loser, he is too powerful / Xig-lem is too powerful.
Word of God thinks that is a natural result of throwing an occidental otaku in TV Land: his meta knowledge instantly puts him ahead of Toon World characters. The villain is even more egregious because he is the villain: he doesn't even have to abide by the rules. Seems that an Ascended Fanboy can only be beaten by... another Ascended Fanboy.
Okay, spoiler alert. Linda was a blank slate created by the Goddess to cater to her future savior's likings, that is: she would look like what the chosen human liked most. Also, Word of God says she's an artificial construct that does not age, that's what she meant in the ending: 'I can be whatever you want'.
The heroes are inmediately accepted / rape the canonic plots.
Word of God states that it is because the canons visited are plagued with Friend to All Living Things Idiot Heroes, who don't really mind. Some dimensional travellers appear and want to befriend you? Well, weirder things have happened. For some at least. About the canon derailment... it is not really noticeable if the episode ends with a Reset Button or events just happen in time periods out of canonic plot focus (most of them happen after the base series have ended)
And it is easier to digest if you just think they interact with the characters in a Kingdom Hearts esque way.
The chapters always have a Suetastic Duel Boss until the end.
Word of God wants to add this: what happens when a unstoppable force meets an unmovable object? Yes: the hero and the villain had to be in an eternal stalemate until the end. they are the same person from 2 different dimensions, so they just cant' kill each other. Only when Mike stripped both of them of their powers he could solve matters with good old Talk to the Fist... and then the Giant Space Flea from Nowhere came to steal the spotlight.