Immortality would not be a curse if people learned to live in the present, not worry about the future nor the past, and above all not becoming attached to anything. After all, it is our attachments that brings us misery. Having an immortal human being who suffers from attachments to things would be hell indeed.
Since this society conditions us to link our happiness to the approval/disapproval of others, as well as being emotionally dependent on others, a normal human being would suffer a great a deal when he knows that anyone he is emotionally attached to will eventually pass away leaving him behind.
One great thing that could come from being immortal would be immense wisdom, again, provided the person learns to direct his attention to the present. Because enjoying the present leads us to be amazed by experiences that most people, except young kids, would find mundane. However, becoming a kid in spirit could take more than a 100 years to the average Joe.
Real happiness comes from peace within one's self. We mistake thrills and wants for happiness. A healthy person does not rely on anyone but himself in order to be happy.