The first season is the best. After this season, the show's developer Andrew Cosby left, and the new showrunners have taken the show in different directions that haven't worked as well. The second season started off well but deteriorated by the end, and the third season so far has been mediocre, with too many characters and threads having been dropped and the new ones not being as engaging.
One of my least favorite changes since S1 is to Jo. She started out as a slightly cliched "tough babe" character, but was still strong and engaging, and when she let her hair down (literally and figuratively) and showed how gorgeous she really was, it had a real impact. But starting with the second season, she's lost her teeth and has become defined almost solely in terms of her romantic relationships and her allure to the men around her, which is much more stereotypical for a female character.