It seems to me that if human beings were naturally immortal, then we would be mentally and emotionally tuned to endure immortality. However, if tomorrow we all suddenly became immortal, well, things could get hairy. The idea brings to mind a few different works of fiction.
The first is Tolkien's The Silmarillion. Death is described as a gift to men, and is incomprehensible to the immortal elves (from whose perspective the book is written). I think this is mostly discussed/referenced in the story "Akallabêth". Persumably, then, it's also a gift to the various other mortal races, and avoiding death leads to problems, as referenced in at least the film (and perhaps the book--haven't read it in years) The Fellowship of the Ring, in which Bilbo Baggins, his life having been extended by his possession of the One Ring, reports feeling "thin, sort of stretched, like butter scraped over too much bread." I wonder if this would happen in reality. I know that the elderly have often told me they're ready to pass on, though that's usually in the context of increasing frailty and illness, rather than simply because they feel they've lived too long.
Then there's Roger Williams' novella, The Metamorphosis of Prime Intellect, the premise of which is that an artificially intelligent computer has discovered how to manipulate and control reality itself. As it's been programmed to follow the Three Laws of Robotics, it makes sure all human beings remain alive indefinitely, living in their own constructed paradises. The story follows a woman who was on the verge of death when this technological singularity occurred, and dislikes the results.
Lastly, and more trivially, there's Wowbagger the Inifinitely Prolonged in Douglas Adams' The Hitchhiker's Guide to the Galaxy series. In contrast to naturally immortal creatures, he became immortal due to an accident, and doesn't cope well. To keep himself busy, he decides to insult every sentient creature in the universe.
For myself, having thought about life and death for quite some time, I think I'd love to be immortal. There would be time to learn anything, do anything, be anything, within the realm of human potential. Even if it were just me, and I lost loved ones, well, I've discovered I can live with that sort of loss, though of course it's very painful. Regardless of what problems arise, so long as there's life, there's hope. Immortality would be wonderful.