I am confused. In the Koran, hell is described as a place of suffering/torment and heaven is described as a place of delight and pleasure (physical pleasure - wine and women, in fact).
You believe that the Koran is the original 'word of God' without human modification or additions, and yet now you say the Koran can be ignored in favor of Bahaullah's writings about hell and heaven?
This previous post explains part of the misunderstanding of how ancient scriptures can be understood in the light of the evolving Revelation in scriptures. The issue is how literal ancient scriptures are considered in the Baha'i Faith. For example the Creation as described in the Bible cannot be considered literal scripture.
The Baha'i Faith considers Hell symbolically as being distant from God in this world and the journeys in spiritual worlds beyond this.
The qualification of 'What is the word of God?' is different from what each individual religion believes in their own scripture. The Baha'is believe the scripture is written for the time of the inspired by God. Revelation, and not literal scripture. Revelation evolves of over time and changes. All the Holy Books are part of the evolving encyclopedia of Revelation from God. They contain inspiration for life, but also contain human beliefs concerning their world and culture.