A lot of people (myself included) would argue this is the best DS9 episode.
I think the Sisko/Jake father-son relationship is a key part of what makes DS9 different to other Trek - DS9 was about putting down roots in a place with everything that entails, in contrast to TOS and TNG being about a ship going from place-to-place each week, and multiple senior crew members having their families prominent in the show was a part of how they emphasised that theme. The Visitor is the key episode of the Sisko/Jake relationship and hence a key episode in what makes DS9 different.