Well, the acting is not as good. Nor is the story or the villains. The Batmobile has nothing on the new one and Alfred is good, but not Michael Caine good. But if you can get past all those "minor" details, it is better in high definition.
The movie is so dark but yet vibrant. The colors just shoot out of the screen when placed next to the deep backs that is characteristic of the Batman theme. Batman Begins is an amazing story and a brilliant movie but Batman and Robin just looks amazing in high definition. Next time it is on HBO HD, your HDTV will look great!