Here's my thing with Sticker Star. Yes, most of the hate comes from fans who wanted it to be like the old games. And yes, if it weren't a Paper Mario game, it probably wouldn't have been so disliked. But I disagree with the idea that anyone who hates it is just "nostalgia blind", and that all of the complaints boil down to "it's not like TTYD so it's bad".
I've never played the first 2 Paper Mario games, but I still think Sticker Star has problems. Things like the lack of EXP, cryptic puzzles, and tedious boss fights have nothing to do with the old games. Even if Sticker Star was a new IP, and had no connection to the Mario brand whatsoever, I would have the exact same complaints for it.