So I finally finished Mushoku Tensei, it's really long and I went through it slowly so it took me literally over 6 months.
It really shines in the scenes where it goes to another characters viewpoint, that's when you see the depth behind their background and their emotional struggles and reasoning behind their actions and get to empathise with them, and it's well supported by the setup for it in the main story so it works really well. Like, my favorite part of the entire story was when it switches to Eris's POV after MC going on a long journey with her and she talks about how much she grew to love him over the journey and how much she was saved by him and how she doesn't feel worthy of him, and you get to see the entire journey arc in a new light and feel for Eris, it's really good.
On the other hand the worst parts are when it's just "things happening", it's just a sequence of events which aren't described in an interesting way so while they make sense to the plot they're not enjoyable to read. Like across the story MC develops a series of dolls and then starts selling them across the entire world in each country they go to, and it's just like boring, you could cut that entire plotline and nothing of value would be lost. I guess it's a problem with the writing style and also with the pacing, so it's pretty inconsistent.
As a former fan of epic fantasy as a genre I also found the plot pretty anticlimactic, it just wasn't grand and large-scale enough for me. It kinda feels like an RPG on that it's just a small party going on a journey defeating a series of bosses and completing quests, no massive wars or super complex plots, each fight is just a small group vs a boss usually. I guess the best in this respect was the queen arc which had some reasonably complex politics and a really cool last fight, but it's definitely not at the same level of "real" fantasy which was a little disappointing.
The characters have good development and most of them get a good little arc but I don't think the author did enough with them? Like Eris got a really good arc like I said above, some very solid character development, and if it was continued across the whole story it could've been amazing? But instead once her arc ends her "role" is just over and then she's just a character who is just there doing stuff, helping out and everything but her arc is very firmly over, and it just feels like a waste.
The same goes for the setting? You develop all these cool little countries and history and stuff, you go to each country resolving their problems and everything, and then the story ends? There was potential here for a grand global war where all the countries unite against the enemy, or a massive collapse of civilisation where everything we've done goes wrong, but nothing happens. Like it's kinda worldbuilding for worldbuildings sake rather than as development for something, I remember reading their journey across the continent thinking "I can't wait to see what he does with all these countries and politics and everything", and then apart from briefly visiting them again for 1 page he does nothing with them.
Basically as a fantasy novel compared to the kind of epic fantasy I'm used to it's very disappointing, its value is as the novel equivalent of a charage with the good character arcs. So if you think of it as a bunch of mixed arcs, some really good and some kinda ok at best, it's pretty good. I don't think I'd recommend it over like, good LNs, but as narou novels go it's probably worth reading? I guess I'd need to read more to know how it compares.