Well the first 150 chapter is excellent. The pace is quite balance, not too fast nor too slow. It's about the rescue his classmate. It's also including the problem of harem. As of c502, MC has 4 wives officially and 1 to be wives soon.

The first three is quite fast to achieved. The fourth is taking a long time to time, not to mention the fifth. It's a bit of drama with the fifth.
After being rescued, the story is go downhill. I'm not saying it's bad. It's more like from excellent to good. Since it's more about how to return to original world, the consequences, and the psychology being isekai. It's become drama oriented. This is also the start where MC truly start exploring the isekai world.

This is where it becomes hectic, it's jumble the story. Problems keeps popping up one after the other, not just on MC but also on side characters too that choose to stay in the isekai world since they've been flashed out more in c400 onwards, especially Yagi, the glasses classmate. There's Meri (female character that's introduced around c420) that adores Honmiya (a girl classmate that choose to stay). There's indication of yuri. There's also a romantic interest of other side charater that died and reincarnated as a child. The more story progress, there's a lot of question that need to be answer. There's no clear main villain yet, there's also no god that fit in the story even though there's a church.

So I'll just wait until the novel is complete.

As of c502, MC has 4 wives and 1 soon to be

Yuika (the Saint, class rep, Japanese person, also an insider for rescue operation, that's why she also has a lot of interactions with MC)

Manon (ordinary Volzard girl, has a lot interactions with MC after he's arrive in Volzard)

Beatrice (Volzard lord 2nd daughter, being saved from dying because a disease),

Serafima (princess of Balsahnia, peeping her while she's asleep, and according to tradition she needs to marry those who sees her sleeping figure. The guards is ridiculous strict though, but MC is OP, and Serafime is the brain in royalty.)

and the soon to be is Camilla (princess of Resenburg, the one who summon MC and his classmate, she's not exactly a villain at first, also she almost died 2 times and almost r*ped 1 times, basically she's a good person but her surrounding is just worst, that's why she's appeared villainy at first).

There's some girls that aim the MC, well actually there's a lot, but this is with highest possibility and interesting in my opinion:

Meisa (the daugther of his boarding house, she truly loves MC, but MC think of her like little sister, because she's just 10 years old and have 0 s*x appeal. Her dreams is to be MC bride.)

Watanuki (MC classmate, her past is dark, she's been r*ped by 3 knights for 2 months before finally being rescued, become desperate, hence she's become slutty after being rescued. She has relationship with few classmates and have s*x with them and become pregnant. She's been helped a lot by MC, financially, mentally, it's almost like a husband. MC is also willing to do anything for her, like hit the boy who abandoned her after he knows that she's pregnant, comforting her cry after being abandoned, doing cruel things to those 3 knights, even killing them, if Watanuki wants it, those 3 knights is beheaded though by Camilla knights, extort compensation from Resenburg for her, and so on. She actually want to be MC wives, but even if she's being chosen, she's believe it's not 100% love, but half of it is pity. She also decide that she's can't choose any other man than MC until she can be proud of herself)