We went through a part of Croatia last year (the northern part), basically from Secovlje through Istria along the coast (Umag, Porec, Vrsar) and then crossed over Istria to Brestova, Ferry to Cres, Ferry to Krk, then to Rijeka, from where we flew home.
What I cannot recommend ist the Istrian coast. The road is very busy, especially with caravans and mobile homes (I'm ashamed to say, most of them from Germany). And the campgrounds in Istria we didn't like at all. The location of most of them on the coast was often great, but I have never seen such large campgrounds... And in one of them we even got robbed, which is not uncommon, as we were told.
Something we really liked was the little bit of island hopping we did. I absolutely loved Cres and Krk wasn't bad either.
Hope that helps, have a good trip!
Kathrin