I think the "wonderful" part is the travel and sightseeing you get along with the cruise. Its about destinations.
The Med cruises are wonderful because you get to see Europe, including the Greek Isles, Istanbul, Ephesus, Athens, parts of Italy (usually Rome, Naples, Florence and Venice), Barcelona, Monte Carlo, and a lot of other great places.
Caribbean cruises are more about the ship for me these days because I have done so many. I don't find the islands all that exciting anymore.
I was only surprised by the Black Sea because I haven't been there and if you compare the popularity of the Baltic to the Black Sea, the Baltic is far more popular. I personally want to go there. I LOVE seeing the old Iron Curtain countries. My Russia River cruise was amazing. I was just surprised because I don't see that many people rave about the Black Sea.
I highly recommend going on a Holy Land cruise that includes the Suez Canal to Jordan. That is how you get to Petra (in Jordan) and also how you get to the middle Nile (stop at Safaga on the Red Sea and take a two-hour bus ride over the desert to the Nile).
Right now I really want to see Asia, but I want to see the modern Asia like Japan, Singapore, Hong Kong. My China trip was not so great.