Memnoch, I agree with a lot of your points.
As far as actors go, Temuera Morrison was superb - I too thought he was excellent in Once Were Warriors (which is an OUTSTANDING film, of course it was sidelined here as an 'ethnic' film
some things never change). Ewan McGregor is an excellent actor, I can't think of a single thing he's done badly - Shallow Grave and Trainspotting are amongst my favorite films. Hayden Christensen sucked bigtime. You are right, no chemistry between him and Natalie Portman (I thought she was good in Leon, despite her youth), their romance was completely unbelievable. People in the cinema actually laughed at some of the lines, not a good sign. And his 'dark side' moments just weren't dark enough.
The criticism I had on leaving the theatre was that there wasn't enough depth and intrigue to the plot. We could have done with more twists and turns, a couple of side-plots to keep up the suspense, that sort of thing.
The scene in the robot construction place on the conveyor belt was a bit too Indiana Jones for my liking. Not that I have anything against Indiana Jones, but there's a time and a place. Similarly the 'car-chase' scene (for want of a better description) at the beginning seemed to be lifted almost straight out of Besson's 'The Fifth Element' - did anyone else think that?
Having said that, it was the mass battles that made the film for me, and they did make up for the nitpicks I have about plot and acting!