Late post for my Croatia trip last year:

DoubleTree Zagreb - upgraded from standard king to their king corner suite; gorgeous room (booked on points)
Hilton Rijeka Costabella - upgraded from standard king to the Costabella Suite w/ balcony and sea view; also a very nice room but not their nicest suite
Hilton Imperial Dubrovnik - booked using a combo of points and free night certificates (standard King); upgraded to their Deluxe Suite with Sea view - this was a very generous upgrade and actually may be the nicest view in the whole hotel; it is on the corner of the hotel and we could see both the Dubrovnik old town and the sea

More recently:
Conrad Las Vegas - booked a standard king room and was upgraded to the "strip view one bedroom suite" - it's a very nice suite but the strip view is lame from this location