Not as sweet as you are used to (or else it has to be declared as "sugar slate", not as chocolate), but richer in taste. And in many more different tastes, now that sugar doesn't cover them. Various different fillings - almonds, hazelnuts, rice, coconut, malaga, something with rum, with cherries (and rum).
Maybe not as good as Swiss, and not as good as it was in SFRY, when there was more competition (!), but still good, and IMNSHO miles ahead of Hershey. Nowadays there are small shops, too, where they make their own stuff, with surprisingly diverse recipes. Watch your weight!
Um, one thing - you'll find nice packages of something called "praline". The word is supposedly French, and so the recipe should be, but it's just little lumps of caramel covered with a thin (and not too good) chocolate glaze. That's the cheap stuff you're supposed to give as a token gift when visiting someone after a long time, along with 200g of coffee and an optional bottle of fruit juice, wine or a good stiff drink.
Update 2014: several brands of once popular chocolates have gone to the dogs - "Najlepše želje" and "Milka" among those I've tried, they have substituted about two-thirds of the cocoa content with some chemical from the Ennn list, which kind of preserves the taste but reduces the fat (rubbish, it tastes close to chocolate only on first contact, but causes throat contraction to me, I take care to have coffee at hand for relief). At least there are Ghirardelli-style darker chocolates with 50% or more, with less sugar. And some croatian imports are the right stuff (for now, will keep reading the small print on the back).