To watch the world waste away and see if humanity ever wipes itself out or comes together and survives possibly even reaching the starts.... Hell yes I'd take immortality... note to self though... bring a razor a sword and a sharpening tool.
There are pros and cons, honestly... Yes, it would get boring after a while and you might get depressed.. but at least you wouldn't have to fear death and stuff. And you'd have a lot more time to do stuff. xD