I have visited quite a lot of Hindu temples over the years. For me, the Sun Temple is unique because it takes the form of a huge chariot (the surviving structure is still 30 meters high). The architectural style is typical for Odisha but different from those in other parts of India. Highlights are the stone carvings depicting Hindu deities, animals, and scenes of daily life (including some erotic ones). There are also 24 beautiful stone wheels, each about three meters high.
Around the main temple there are ruins of minor temples and buildings. But all in all, the area of the site is small. My visit took about an hour. There is also a museum run by the Archaeological Survey of India just north of the temple. Unfortunately, it was closed when I was in Konarak in 2016.
The Sun Temple is the biggest tourist attraction in Odisha, and it can get very crowded. The site is easy to reach by public transportation or taxi and can be done as a (half) day trip from Puri or Bhubaneswar. As with many World Heritage Sites in India, the entrance fee for foreigners is quite high but in my opinion worth it.
If you do not get enough of ancient temples, there are more in the area. The Ekamra Kshetra of Bhubaneswar (THWS) has dozens of temples in similar style, however none as impressive as the Sun Temple. Moreover, there is the Jagannath Temple in Puri, which is an important pilgrimage site but only open for Hindus (for a small donation you can have a look at the temple from the roof of the library across the temple entrance).