It's funny, my appreciation for the film has followed a trajectory that is the exact opposite of your's. During my first viewing I was so distracted by the hackneyed plot, one-dimensional characters, and sometimes absurd dialogue (specifically the political sound bytes) that I couldn't enjoy it. As time has passed and as I have reconsidered it, I now love it and appreciate it for what it is.
Originally I was too distracted by the above points to appreciate the world that Cameron created. I think Avatar is too often praised merely as a technical achievement in this regard, while I most appreciate the work that went into sculpting the dozens of species of flora and fauna as well as the geology of Pandora. When I try to explain the movie to those that haven't seen it (yes, such people exist), I describe it as a movie set over the documentary Planet Earth, yet all of the gorgeous scenery is fictional, yet fully realized.
And as far as plot and dialogue, I have come to consider it almost as a fairy tale. Yes, it is simplistic, but this allows for some fantastic moments. I think of the scenes in which Jake world view evolves all the time- specifically the scene in which Neytiri scolds him for celebrating after she saves him from the viperwolves.