This is a pretty meta series.
Originally, this kind of story is that a boy and his friends are taken to a fantasy world where they battle a great evil, growing stronger after each conflict and challenge.
Then the stories become one kind of LN cliché and the boy is immediately OP. It's turned from moderate wish-fulfilment to a cheat-code user's dream of someone who hacks into the gibson and takes over the story by using a trainer. Mushoku Tensei comes to mind.
(Then you have the stories where the main character is underpowered and has to become Batman, which are better on average...)
But here.
Here the ostracized otaku, who is hated because the pretty girl in his class actually pays attention to him, here he is taken to a fantasy world with everyone that hates him (+ the girl and some other people) and becomes the weakest of the weak, has a crap crafting style class and a cynical outlook on how the story of this particular world will turn out to be.
So the author lets him fall down into the abyss in a dungeon in almost the exact same way Gandalf does and turns the boy from an underpowered crafter into a demon-flesh eating hax-machine with 10000 in every stat and skills up the wazoo and a vampire waifu he saves and his hair turns white and the mighty HERO who came with him maxes out at a bit over 1000 and he creates a gun using fantasy minerals AND IT'S ALSO A RAILGUN, also it's a revolver...
Every single thing I wrote there is true. Not a single ounce of hyperbole. The 10000 stat thing IS CANON.
How many layers are here, people? How deep are we in the rabbit hole? It's not a question about suspension of disbelief ("he succeeds at this because he finds a magical jewel thing that seeps out HP+MP potion yadda yadda it's a super rare thing that hasn't been seen in a gazillion years etc. etc.") it's about moderation.
Sure, make your MC op if you want, but this, this is just obscene. This author isn't just a first level otaku-wish-fulfiller, he's up to level five. People who hate him because an otaku -> they are defeated by the otaku mwahahaha x a million.
In addition to this, the text is about 40% exposition about things the main character has no knowledge about. There's no sense of mystery or discovery. I won't comment on the writing itself because it's filtered through unedited translation.