The country I think I found most intriguing, however, was right across the border from Italy: Slovenia is breathtakingly beautiful and the people there (at least, the ones I interacted with) were very friendly. Again, it was a visit of only a few hours, and we ultimately decided not to make a second trip into the country to see the capital of Ljubljana (not enough time!), but right now Slovenia is at the very top of my "GO BACK!" list.
Anyway, below is an updated list of countries I've visited and the years I've visited them, with the most recent visits denoted in red. If I didn't stay overnight in a country - e.g. a order crossing, an airport stopover where I left the terminal, or a cruise port of call - the year I visited is italicized. Nations with an asterisk (*) next to them are among the world's 25 smallest countries, of which is my life's goal to visit all of them before I die. Having spent the night in the picturesque (and ridiculously expensive) Principality of Liechtenstein during this most recent trip, I'm now 20% of the way there.
Antigua and Barbuda*:
1974, 1980, 1982
1988, 1989, 1990, 1993, 2001
1979, 1983, 1986, 1987, 1989, 1995, 1997, 1998, 1999, 2000, 2003, 2004, 2005, 2006, 2007
The Kingdom of the Netherlands:
2006, 2008, 2012
The United Kingdom:
This past summer's travels get me up to 20 out of 206 sovereign (or de-facto sovereign) nations, or 9.7% percent. Still not great, but I'm making progress.
(Flag source: World Flag Database)