I am from Croatia,
been in Dubrovnik only twice, but I must warn you it is overrated

now, in summer, you will not be able to walk through old core of the town,
that is how much people crowd the place,
prices are really high, don't get shocked,

pictures online are the best you can see, taken in special places and times of the day and season

for Dubrovnik, you can safely apply the same proverb as goes for Mt.Fuji,

"A wise man will visit Mt.fuji, but only a fool goes there twice"

don't get me wrong,
Croatia, summer, sea coast in general, you can't miss, but don't get expectations too high