I dunno. On one hand, being immortal would be really interesting. You'd be able to witness the progression(or regression, I suppose) of mankind. You'd be able to know that which is unthinkable nowadays.
On the other hand, all those people you knew and loved... gone. And you're destined to repeat that process again and again and again until you end up completely withdrawing and becoming "that creepy old recluse" to all the neighborhood kids, who become adults and get old and die all while you try to get some sleep in your ramshackle abode and yell at them to "keep that racket down you lousy brats" while muttering under your breath about how the kids in your day, which was something along the lines of a few centuries ago, as far as you can recall, you can't really remember too well anymore, were so much more well-behaved and would have never gotten on the elders of their time's nerves so much. After that long-winded rant, you'll probably start complaining about how horrible their grammar is and how they always use so many run-on sentences and how they smell funny.
Or something like that. I probably should go to sleep now...