People keep saying this and I don't get why. People have outlined the issues with Sticker Star in detail a number of times. It's a very odd game with mechanics that are at odds with each other.
- Combat requiring stickers but giving the player little to no reward in return, thus making it 'better' for players to avoid combat entirely being one of the most glaring. The game discourages interacting with the combat system
- Lack of challenge associated with the combat. Most bosses come down to using a certain sticker to knock off a tone of their health in one hit, which isn't much of a fight at all really.
- A lot of the puzzles (ie, find this place to put this sticker) are kind of obtuse and it's not a lot of fun to wonder around looking for "Solutions". Once you find the solutions they aren't really puzzles at at all, they're just just "put this thing here" 'puzzles'.
- The lack of quality writing to push the player forward despite the weaknesses in the gameplay department.
I'm not against the idea of Sticker Star - and I actually really liked Super Paper Mario, so I'm not afraid of change, but Sticker Star is heavily flawed no matter how you slice it.
Also, people are just reacting to what we've seen. There are a lot of elements here that are very similar to Sticker Star so naturally people are worried that it will be flawed in a similar way. We saw that the battle system is similar and that a mechanic nearly identical to Stickers exists as well. It's fair to react to that.