Not driven but flew and hired a car (not cheap compared to other countries) last year.
2 Weeks - Flew into Split, stayed Omis, visited Trogir a heritage site worth visiting. Then stayed Plitvic Lakes which are fantastic and needed two days. Then back down to stay Makarska which is a town of two halves one end very touristy other end lovely town square and boats, we did a boat trip to the islands which was good (beware some boats loud music and drinking, other more sedate. Then stayed in Cavtat and visited Dubrovnik. Agree with Mr Plodd Dubrovnik is a must to visit, can be very very busy if cruise ships are in, we went in August and were lucky not too busy. Took boat taxi to Dubrovnik, apparently parking is awful there. From Cavatat we also drove to Tresteno Arboretum which is very quite and nice, they filmed scenes for Game of Thrones there, also if you go there drive right down to the bottom of the windy road to a small old fishing port, pretty and an interesting deserted building. Then from Cavtat we drove back to Split Airport.
Didn't go into Split, looked very industrial.
Loved Croatia and planning to go back, this time with van and visit the north west, Rovinj, visit Zagreb and probably back to the lakes but would plan about 3 week trip.