Simply put, it took away many aspects that people liked about the previous games (partners, original characters, badges, a leveling system, any sort of story beyond the absolute bare minimum etc.) and added things that people didn't, like a battle system that revolves entirely around consumable items, and it marked the beginning of a general change in the series' direction that fans weren't happy with. To add insult to injury, early footage shows that it was planned to be closer to what people were hoping for.
I didn't hate it and don't dislike it either (which causes me to have a vastly different opinion from quite a few Mario fans), but it is definitely the weakest Paper Mario game I've played (compared to Paper Mario, Super Paper Mario, and so far Paper Mario: The Origami King) as the worlds (EDIT: and even more so characters and story by far) are not that original sometimes, and there isn't motivation to battle normal enemies at all as you use up stickers, the only reward being coins to buy more stickers. That being said the game is still fun, just one of the by far weaker, if not the weakest Mario RPG.
It's probably the Mario franchise's most overrhated game, but a lot of it stems from the sheer disappointment of the final product we got and much of the fanbase who adores the first three games in terms of consistent setting, structure, and characters. Sticker Star isn't a bad game in of itself, but because the changes directly affected what people loved about the first three games in a negative manner, it became a little bit personal, especially seeing like recurring characters such as the cooks, partners, Merlon clan, etc, get replaced by generic Toad NPCs.
Is the hate justified? Some parts, no. Too much people blame a named person behind this, whether it's Miyamoto or Tanabe while ignoring the faceless execs who additionally play a role in shaping the Paper Mario games into what we know now (such as when Tanabe mentioned that the developers need to stick with a consistent brand recognizability with their characters and thus can't edit the physical attributes of Toads, Koopas, etc any more). Does the dislike of the game come from a reasonable place with reasonable expectations? Yes.
Simply put, it marked a very unnecessary directional shift in a series that I thought was going in an amazing direction before it. The previous game had the highest stakes in the franchise with all of reality on the line, the best cast of villains in the series, and the heaviest story with undertones of death, loss, and grief. The previous game before that was also very dark by Mario standards, took Mario to incredibly interesting and subversive scenarios, and had perhaps the greatest NPC cast the franchise has known. It also had best girl, Vivian, who deserved to be a mainstay in the series.
Then for absolutely no good reason, they pulled it back, and not just a little bit, they outright went complete 180 and turned Paper Mario into just another generic Mario game in terms of world and characters. They could have just made another game like the original Paper Mario where it's in the Mushroom Kingdom and Bowser is the villain but the world is rich with characters good and bad that aren't necessarily all base designs from the platformers.
The interviews where they speak so proudly of what they did to the series pissed me off, and with each new game, though the games themselves were improvements over SS, came new interviews hammering home how permanent the changes in SS are. Now, Origami King is a genuinely good game, but the interviews surrounding it were downright depressing to read. All these "Since Paper Mario: Sticker Star, it's not possible to modify Mario characters (no more Goombella or Bobbery etc) or create original characters that touch on the Mario world (no more Vivian, Doopliss etc)," and it's also "no longer possible" to visually portray age, gender, etc in Toad NPCs when those are literally the things that made them so interesting in the first two games.
Sticker Star is the most sterile game not only in the Paper Mario series, but the RPGs in general with the possible exception of Paper Jam (a game I have similar gripes with). It basically directly and intentionally avoids every design element that defined my love for Paper Mario, and it has far more influence on the current series than any of the previous games, that's why I hate it.
All that aside, the gameplay design is also very poor. I could forgive that if the story & characters were on par with the previous games (SPM doesn't have the best gameplay in the world either but I still adore it), but with nothing to distract from it, it's even more glaring. The lack of EXP means there's no point to battling. You just get coins and stickers, both of which are littered around the world for free. The battle system provides no "free" attack option (the equivalent to the basic Jump and Hammer in past games that used no FP) so it's entirely possible to run out of attacks altogether (though improbable given how you're unlikely to use more stickers than you gain). There's also the poor puzzle design, making bosses puzzles and making it not only possible but likely for a player to stumble into a boss fight without the item the game expects you to use to defeat it, which is often located in a random unrelated place in the world and entirely skippable. With the weakness item, bosses are almost impossible to lose against, negating the challenge. But without it, they're nearly impossible NOT to lose against, which also isn't a fair challenge. Compare that to previous games where each boss could be tackled in a different way each playthrough with many possible builds and strategies to offer a unique experience each time.
This analysis does an excellent job of summing up most people's gripes with this game. It's nearly 4 hours long so you'll need to buckle in for a while to watch it, but trust me, the time is well spent to comprehensively break down this game and explain why it's flawed.
It really isn't, it's just very bad by Mario RPG standards and in terms of that Nintendo has had a boner for repeating as many flaws as possible in Sticker Star in every Mario RPG since, except for maybe Mario & Luigi: Dream Team.
sticker star is one of the two paper marios i havent played, so take what i say from an outsiders perspective
the mandates are baffling, like, i get that miyamoto wanted to make it simple, but.......why? if anything, since the previous 3 did as well as they did, i dont see the point of changing how everything works. the gameplay being different is honestly weirder since there were no mandates regarding that, and im just talking about the disposable weapons, and rpg doesnt need exp to be fun. i mean im glad that origami king is making a change for the better, removing most things that made sticker star and color splash as polarizing as they are.
i cant call sticker star a bad game since i havent played it, but a lot of the decisions theyve made make no sense to me
"Hey guys let's make sure each new Mario RPG only has things in common with the most unpopular Mario game of all time, instead of being at least closer to the first three games which people actually liked, and for valid reasons"
