Apparently for the bosses, if you have the right sticker, you win the whole fight. If you don't, it's total torture.
The only experience I have with this is Bowser Junior, who couldn't be beaten unless I had the Scissor sticker. I tried with as many stickers besides the scissor that I could, but he killed me every single time. The other bosses I couldn't play, because I got lost due to lack of direction and had to give it back to my brother. I just couldn't play it anymore.
My brother, on the other hand, loves Sticker Star. Like, I've shown him Paper Mario 64, I've shown him The Thousand Year Door, I've shown him Super Paper Mario. He said that "they suck comapred to Sticker Star". He also believes that PM:SS is the best in the series and that Kersti is better than all the partners. He's 9 though, so as he gets older he'll probably learn that Kersti sucks and that he should worship the first 3. He'll also probably learn that pushing me into everything at full force isn't the best idea and I might go to the hospital