First of all, the movie was o.k. The special effects were pretty awesome, and the action seens were o.k., although sometimes they were too fast to see what really happened.
The plot, however, was questionable and unsatisfactory. Too much talking, he didn't get the girl, he was never told about the plot to make him hurt, etc. Too many loose ends. Did the girl ever get cured? We don't know. Did the blond fail class? we don't know. How could the explosive devices only scar the face of Harry, but completely disintigrate the black goo, which was heated to thousands of degree's when it entered earth's atmosphere? What about the blob that the professor had?
Like I said, if you liked the first two, you'll probably go see this one, but I think the first two were better.