Spoiler
the cataclysmic event in the end is much more violent and features plenty of gore, and I liked its portrayal better there since it reinforced the nature of Ozymandias' actions. Also, the lack of the Hiroshima references and the Tales of the Black Freighter story really made a difference, considering how it developed Ozymandias' background and even hinted that his plan didn't work at all in the end. Also, Bubastis was meaningless in the movie.