It really is a unique creature that many of us absolutely loved.
FC3 really dropped much of what made the game so fulfilling. The interesting setting was gone, replaced by a 'seen a million times' tropical setting. All sorts of 'game-y' elements were added that litter the screen. Unnecessary RPG-like progression. Overboard collect-a-thons. Map was relegated to the menu again.
Basically, they tried to widen the appeal and took away much of what made FC2 special. I still enjoyed FC3 to a degree, but I will always hold FC2 in higher regard and worry we wont see a game like it again for a long while.