Just a disclaimer: This is my interpretation of Hell based on my years of study as a Christian and my personal walk in my faith. It is not meant to represent the beliefs of anyone other than myself.

So, what I believe Hell to be is eternal separation from God. God is good, he is perfect, and he is awesome (in the old sense of the word). Personally, I define "sin" as anything that moves you away from God, so if you live a life full of sin, when you pass on, you no longer have the option of undoing your mistakes, or making them right.

Because God is good, perfectly so, anyone who is imperfect, anything that is wrong, anything that pulls you away from him, would be painful for you. If there were sin in Heaven, you would be in constant pain. To deal with this, God barred people who have no made their lives right from his presence. He doesn't want us suffering more than we have to.

For me, Hell is not a place of torment. Rather, it is a place where people are sad, and angry that their choices have lead them to the wrong conclusion. Where they are forever cut away from the perfect good because of their own decisions.

Sorry if that's rambly, I'll edit it later... or at least reread it.