The story continues with Anakin Skywalker, and how he finally becomes Darth Vader. The film lacks focus because it is going from place to place and we see characters who we don't really know. The mainframe of the story is Anakin to Darth Vader. Not that fight between Obi Wan and that weird robot thingy that can fight with four light sabers.
Once again, George Lucas dumps too much CGI in the film, as well as shitty dialogue, painfully long light saber duels, and horrible romance scenes. It is hard to fathom how bad this film is. I guess people lowered their expectations from the previous ones to see a quality film.