Weeds has a very strange character arc. Nancy certainly overcomes obstacles, but she doesn't become more heroic as a result. Each time she bares a bit more of herself, and it reveals a more complex fleshed out human, which is very believable, but not necessarily more likable. Clearly the show runners are aware of this, whether by design, or if it just became apparent along the way, and they decided to lean into it.
It doesn't make the show any worse. Depending how you look at things, it might even make it better. Kinda depends if you're an early seasons purist and you just like the goofy side of the show, or if you're in it for the story arc. The first time around, I stopped following around the time Esteban came in. I might've been to young to parse the behaviour; I don't know. That, or maybe I just wasn't into the tonal shift of the show during that season at the time.
Anyway, I'm glad I'm making it through it now. If anything, because Kevin Nealon somehow sticks around to the end, and that guy is fucking hilarious (though it turns out he's even funnier out of character; his appearances on Conna O'Brien Needs a Friend kill, especially in video form. If you don't know what I'm talking about, look up "Kevin O'Nealon straw bit" and "Kevin O'Nealon Conan tears").