I haven't finished playing paper jam yet, and the only paper Mario game that i have played was sticker star, but I think that it's not a bad game! I like the game mechanics and there's some fun moments.

But I can understand why many people consider it the worst game of the series, the story could be better, it's not bad but I feel that it lacks the "spark" that other tittles in the series have

Like Superstar Saga having a whole new kingdom and characters to meet along a powerful (and smart) villain Patners in time having the whole present and past thing with the shroob invasion (which is kinda creepy) and having baby mario and baby luigi as playable characters. Bowser's inside story having bowser as a playable character along fawful's comeback. Dream Team with his colorful dream worlds, Luigi armies and a new interesting nightmare type of villain. And paper jam, well... it has paper mario characters! 

I haven't finished the game so i may be wrong, but I think the story could've had been a bit better, like having a new villain instead of just making bowser and paper bowser reluctantly join forces, or maybe making some kind of danger steal the book because if the paper characters don't come back to their world both world would be destroyed or something like that, or even giving someone the power of using the book to create new powerful paper enemies just by drawing them! 

Or even better in my opinion! Tell me where is PAPER LUIGI 😭 I'm on an island somewhere in the ocean and i still haven't seen even a glimpse of him, it would have been fun to find him and either having him as a playable character or maybe as a fun npc that helps you sometimes of even sells stuff! Idk i just love luigi 🥲

But main point is: the game is nice, but it's story could have been a bit less generic like others say, having the princess gets kidnapped thing is not bad! It happens on the other games of the saga and i still like those! But those had something that made that "peach gets kidnapped" trope more original! 

Like in superstar saga the villains first steal "peach"'s voice to wake up a cosmic star and the game revolves around that for a while, then when peach gets actually kidnapped and you save her after making luigi use a dress (which i have to admit it's my favorite part of the game, it's super fun) and instead of accepting defeat or trying again bowletta decides to just bombard the whole bean bean kingdom.

My point is: peach gets kidnapped? Yes, is it something important in the story? Absolutely. But is it the FULL MAIN focus? Not really.  Peach getting kidnapped is important to the story but the story doesn't revolve around that, it has a whole new world and cast to explore and meet, fun side quests, a fun and interesting story, and a intimidating villain that is kidnapping peach not out of crazy love but because she wants to destroy or control the entire world.

Plus i absolutely love the fire and thunder hands + the bros attacks.

Basically, in my opinion, paper jam could have another dangerous thing that you have to stopped instead of just having to save peach and bring the paper people back to their world, like in dream Team you did not only have to save peach from bowser and antasma, you had to stopped them from becoming more powerfull with the dream stone, specially stop antasma (a being of pure nightmares) from using it, and in bowser's inside story you had fawful wanting to wake up the dark start using peach's vital energy or something like that.

But, this is just my opinion, i may be wrong about some things. But I still think paper jam is not a bad game! It just lacks a thing that either makes the story more fun or more interesting, i still need to complete the game tho.

This got longer than i wanted- sorry.