Hi doremifaso
Speaking from own experience altho it was many years back, i find Candi Sukuh is truly unique in its own. Imagine a step-pyramind in this part of the world & very similar to the famous Aztec's albeit on much smaller scale.
My 1st visit began with this Candi Sukuh, then move on to Prambanan and ended with Borobudur.
From the smallest unknown to the most famous candi, there was this overwhelming mix of expectation because amazingly, Sukuh didnt disappoint me although it is not famous, not big and in a remote mountain area.
Next, it was Prambanan (never heard of it b4 this). Boy, if you approach Prambanan from the front and far, the sight is just wow! First thing came to my mind then was, how they built it?! This was before the earthquake in 2006. We were still allowed to went into each 5 main buildings

That night itself, i went back to Prambanan for the Ramayana ballet with the candi's as the backdrop. It was just magical that night. The setting & the performance were easily of highest standard. ** I didnt know it was more than 2.5 hours show with a short break in between
That night i began to worry. Was Prambanan the highlight of my journey? What about Borobudur? Will it be less thrilling than Prambanan?
Hehe..at this point..i shall let everyone to decide on their own
If you r the adventure-sort, the kraton complex in Jogja is a must, especially the "mosque". Having said that, since i went to Solo before Jogja, i also having a great time in Solo's kraton. (Almost bump into the royalty

)
Parangtritis beach for sunset view is ok provided you have the time. Is a very run down place. Port Dickson's facility is like 10x better but the view of the Indian ocean, either from the cliff or on the beach..is just differently great!
Have a fantastic time in Jogja