Are we mortal for a good reason or is it just a shortcoming?

There is an “immortal jellyfish” specie out there:http://en.wikipedia.org/wiki/Turritopsis_nutricula

But is immortality really good? What are the good and bad points of immortality? Overall, is it good or bad?

One bad effect would be that on the population, as fewer people would die-
What would happen if we were given immortality in exchange of reproductive abilities? After all, individuals evolve mentally (and spiritually) in their lifetime- we could still have a wiser and reformed society without the natural evolution that occurs across generations.