With long use of SSRI class medication, a person can develop anhedonia. This is because these class medications at some point affect the dopamine levels. As a result, you experience what you call "emotionless" state of being.
Often, to counteract this, a physician may add dopamine agonists to your SSRi medications such as Wellbutrin.
Anhedonia is a symptom of depression and if you're experiencing it, your depression is not per se improving. You don't want your base line to be that of anhedonia (emotionlessness) http://www.ingentaconnect.com/content/adis/cns/2000/00000013/00000001/art00004