The story itself is not to bad, Superman sacrifices himself to protect Metropolis from Doomsday, after the JLA are swept aside by this new foe.
News services around the world reported about the death of Superman, and no comic event since has generated this amount of interest. One of the most recognisable icons in the world was dead.
Of course he came back, three days later in fact, highlighting the similarities with the Christ story.
Have a look and see that heroes can die.