The original movie was based loosely around Kurosawa's The Hidden Fortress. As such it included some wonderful mythological motifs. One of the great themes was that of the Hero Cycle as defined by Joseph Campbell who was one of Lucas’ influences. The other films in the original trilogy had a very strong base to build upon and also introduced some classical plot elements.
Unfortunately Episode I was so weak that the whole prequel trilogy has no foundation. The only mythological theme that I detected was the virgin birth of Anakin. The Force's mystery was also destroyed with the introduction of Midichlorians. It is space fantasy after all. There needs to be some Magic.
I can forgive the cheesy dialog and bad acting, after all the stories are targeted towards pre-teens, but if there are no deeper themes then the older audience members aren't going to keep coming back. I also don't feel emotionally connected to the characters. The highs and lows of the plots have been filed down to mere bumps.
Oh well ... I'll just keep chanting my mantra "The next one will be better"