Definitely worth seeing (I saw it once, and was so impressed that I went back for the IMAX experience). Ledger is amazing, as are the other actors. The stunts and gadgets are beyond spectacular. Establishing shots & scenes shot in IMAX are great - which makes me wish the entire film was this way - but the cinematography is certainly nothing to sneeze at.
Definite Oscars coming this way. See it (in IMAX if possible).
There were definitely some cool scenes in there, but overall I thought the plot was lacking - as soon as the story developed, it was over. I really began to love Will Smith's character but unfortunately the shortness of the film inhibits really getting to know him. I give it 6/10. Wait for the video.