How do Jehovah's Witnesses understand the essential nature of hell, and how does it differ from that of Seventh-day Adventists? Earlier this week, I was talking to a friend, more arguing really, and the subject of hell came up. And he said something that got me thinking. He said "There's no hell as many of us believe it. There's no eternal fire as we're told. There is only death for those who sin." And he went on to quote Romans 6:23, 


  The wages of sin is death (ESV).


So that got me thinking and for the past few days I've been troubled. Like if God really loves us why would He subject us to that kind of torture for all eternity? I mean, isn't He the same God that gave His son to die for us? Isn't He the gracious and the merciful and the forgiving God that stuck with the hard headed Israelites in the desert for forty years?

Now considering my friend is of Jehovah's Witness background, is it possible that that is what they believe hell to be? And how different is it from what the Seventh-day Adventists believe it to be?
Wikipedia has decent information on this topic.  First, the beliefs of Jehovah's Witnesses on this subject:


  Watch Tower publications teach that hell (hades or sheol) is not a place of fiery torment, but rather the "common grave of mankind", a place of unconscious non-existence. Gehenna, the Bible word commonly translated "hellfire", is said to describe a judgment of complete destruction, from which resurrection is not possible. They reason that complete destruction does not allow for literal "torture" of the wicked, as the deceased person is not conscious.


This describes a form of annihilationism that appears to be consistent with what your friend is describing.  However, there doesn't appear to be much difference when comparing these views to those of the Seventh-day Adventists:


  Seventh-day Adventists believe that death is a state of unconscious sleep until the resurrection. [...] They reject the traditional doctrine of hell as a state of everlasting conscious torment, believing instead that the wicked will be permanently destroyed after the millennium.


For more on this, as well as a comparison with other systems of Christian belief, see Wikipedia's article on Christian views on hell.