My main goal is to truly visit each and every country. Not "I was in the airport for a layover for an hour", but truly experiencing each country.
As a general rule, I consider a true experience to be sleeping in a hotel away from the airport/train station and eating a meal. It is a low bar, but it excludes several countries that I have technically been in but never left the comfort of a transportation zone (all English signs, all passengers were security screened, almost all stores take credit cards, restrooms everywhere, etc).
I'll probably never meet that goal due to some war zones and a fairly steady change in the borders/number of countries. But I think I can come close. I'm up to 24.