I think people are being too hard on this game.
I'm nearing the end of the 3rd world, and I'm having fun. the dialogue is still good, and the music is top-notch. Also the level design is great, which is something the first two didn't really have that often.
also, if you don't use the certain sticker that's super effective against them and does like 80% damage, the bosses are pretty hard. the trick is thinking of the Thing Stickers not as a crutch (except for those certain super-effective ones), but as summons. they take up a lot of room in your album (a lot of SP from your mana pool) but do massive damage with a small cinematic.
and despite the game being stage-based, I'm finding it much more non-linear. For example, world 2 was giving me trouble so I went into world 3 and advanced that a bit. I've been going back and forth, and having just finished off the world 2 boss I'm going to tackle the world 3 boss. Also, a lot of the individual stages have multiple exits, and I think every one has a hidden door you might want to go back and find. and then the stages themselves, like I said, are interesting to navigate through.
now, there's a lot that's gone wrong and I really really don't want paper mario to continue down this road. Everything CCC said about the game's world-building and story is true. and the idea that you spend stickers to beat enemies to get coins to get stickers is a cyclical design idea that kinda doesn't work very well, because it encourages skipping every enemy and saving your stickers for the challenging boss fights. and without the ability to select targets or have a two-member party, the battles themselves don't seem to allow much strategy.
but like I said at the very beginning, I'm still having fun. you might be surprised at the range of attacks you can do, it isn't just normal hammer and normal jump. granted, it's nowhere near the variety that happens when you have dozens of badges and half-a-dozen partners, but it's still engaging. I'm honestly surprised that I'm enjoying it as much as I am, but whatever. It isn't like the other paper marios, but if you can just accept that you'll find a game that's still a 6.5/10.