For sure Kill Bill isn't all that deep except in how many different bits of genre it pays homage to. Serinity is similar in having a mixmash of genre, but - I can't put my finger on what makes it better in general. Every comparision I can think of seems to be true for both.

Maybe it's that the Kill Bill Story is one dimensional, the vengence of one person, compared to Serinity's struggles that take place on so many levels.