#9 (but really, it should be #1):

Sweden has one House and one House only.

No voter in the world is more empowered than a voter who votes for One House only in a proportional manner. Very few nations fit the bill, and Sweden is one of them. Yes, all of these One-House nations are part of the Happiest Nations club, sitting in top positions.

Compare this to winner-take-all (USA, UK) and it is understandable that Sweden is organized much better for all. All get to appoint their representative. After the elections, voters can point at the person or party they hand-picked themselves, sitting in one of the 349 seats. The only minor is that Sweden does not have the pure form of proportional, but rather multi-seat districts, but it gets pretty close.

Then, very fortunate as well, there is no additional Senate or an empowered President. As the French say, the more things change the more they say the same, and Sweden does not have to deal with that problem so common in US and UK. Its democracy is very inclusive and relatively direct.

Their voting system results in about 8 parties. Female representatives account for 46.1%.

Systems can make people sick. Systems can make people happy. Sweden is the lucky one with a smart voting system. Hip hip hooray for Sweden.