I just finished Forbidden by Ted Dekker and Tosca Lee. It takes place some 500 years since the human race recreated itself through a retrovirus that did away with all emotions but fear, to prevent the previous emotional states which caused a thermonuclear war and could have wiped out humanity. Now, an unwitting young man ends up drinking a potion that undoes the changes and he is the first person to feel other emotions in centuries. But the world is united in a second Roman Empire, this one encompassing the entirety of the remaining population.
Next up is the sequel, Mortal, by the same authors. Those few who took the potion are now keeping a little boy safe, as he was born (as foretold by a prophecy) with the results of the potion already in his system: he feels the normal (to us) broad spectrum of emotions and will be next Sovereign (world leader) if they can keep him alive to age 18.
Unfortunately, it looks like there is at least one more book after this one, and I picked these two up (for a buck apiece) at a library book sale. The third book may be somewhat difficult to find...I may have to consider an on-line purchase.
Johnathan