Firstly I'd recommend reading the Light Novel over the Web Novel - The Web novel looks like it has been put through Google translate and I think anyone reading it would lose a lot of enjoyment that way.

I've read Light novels 1-3 which I believe is around 75 Web Novel chapters.
This was one of the best light novels I've read but I can understand how it can be subjective.

The story of the first vol (ch-1-25) is about the MC falling into a dungeon with the only way of escape being to clear it. It's story of survival and of how he has to destroy himself and rip away at his own humanity in order to survive.

After vol1 the story becomes something more of power fantasy though of which I found leaps and bounds more enjoyable from other power fantasies. Rather than starting out OP we actually see the MC struggle to become as strong as he is. Though because of what he has been through his humanity is still fractured and so his choices are not what you might expect of an OP MC.

A large part of Vol 3 shows how his heart starts to mend itself, thanks to the characters with him, little by little but because of this he has to take on a heavy burden.

I'd recommend anyone to buy and read vol 1 of the light novel.