living forever would be horrible. you'd see all your loved one's die and if you make new friends you'll just have to watch them die over and over again.
you'd be so far out of time, people wouldn't eventually know anything about our current times. imagine having so many memories and not being able to share them with anyone.
and obviously, as people already mentioned, this planet is going to die eventually (assuming humans don't leave earth)
living a couple of hundred more years would be really nice though