Eric seems to be that Discworld book that was written after Guards, Guards and before Moving Pictures that nobody ever mentions. In fact having a glance over the comments on Goodreads it seems that it is not all that liked, and when I asked my friend who loves anything that Terry Pratchett writes, he simply said that it was okay, it has its moments, but not one of his best. Mind you we both agreed that the part where they travel to Discworld's version of the Trojan War was probably the highlight of the book, though I would have to also mention that the part where the guy whose hell is to endlessly push a boulder up a hill is replaced with somebody reading to him the entire Occupational Health and Safety Act (along with commentaries) was also a classic.
The story begins with Rincewind, who if we remember, was trapped in the Dungeon Dimensions at the end of Sourcery, being summoned by fourteen year old Eric who has the dream of becoming the ruler of the world, marry the most beautiful woman in the world, and to live for ever. We then go on a journey to see these wishes fulfilled in a way that one would expect them to be fulfilled when the wishes are made to a demon (though Rincewind continues to protest that he is not a demon, despite the luggage – I love the luggage – doing its best to prove this assertion false).
Once the wishes have all been fulfilled (as it turns out the whole idea of Helen being the most beautiful woman in the world was something of a legend, though we must remember that over a period of ten years people do tend to age), and Eric has discovered that the fulfilment of these wishes are not what he particularly wanted (sure, you can live forever, but you will begin your immortality at the beginning of the world, and continue on from there). The final leg of their journey is into hell (and we also get to see that road which is paved with good intentions).
Now the idea of hell that Pratchett portrays is very interesting, and he sort of pokes holes in the current idea that we tend to have (such as why is it when we don't have any nerves, or any body, are we inflicted with eternal pain?). His idea of hell, and though he brushes over Satre's comment that hell is other people, is that it is pure, unadulterated boredom (such as having the entire Occupational Health and Safety Act, inclusive of commentaries, being read to you). Personally, I don't think any of us can truly imagine what Hell is really like, except for the fact that it is not a very nice place. Our current idea of Hell, being fire and brimstone, is something that was borrowed from the Greeks, and developed by both Milton and Dante. However, the idea that we exist in Hell in a spirit form is not biblical because the Bible suggests that in Hell we will have our flesh, and thus be able to experience pain. Mind you, one of the best ideas that I have encountered about Hell comes from C.S. Lewis' The Great Divorce: Hell is not so much other people, but the fact that we cannot get along with other people, so we constantly seek loneliness. Not only that but it is also psychological, in that we are forever cursing those who have sent us there, and are so horrified with who we are and what we have done, that while we can see heaven, we simply do not feel worthy enough go there.
I read recently an article in the Australian Financial Review about the idea of hell, and one idea that came from that was that Heaven was Heaven simply because it is not Hell. What was suggested was that those of us that are in Heaven could look down and see the fires and torments of Hell, and the fact that we were not there was what made heaven pleasurable. However that is a very smug and self-righteous view of what Heaven would be like, and to think that Heaven is being able to gloat over the fact that you are not suffering the way others are suffering is almost contradictory to the nature of God. The Bible indicates that God is unwilling to see people go to Hell, but they go their under their own steam simply because they have rejected God's offer. As I have suggested elsewhere, it is like being given an invitation to a party, and turning that invitation down so that on the night of the party you are sitting at home alone wishing that you could go to that party, but not doing so because you said no, and then raving in anger at those people because they are having so much fun (and I say that from experience).