Visitors get the choice of visiting for one day, three, or a whole week. Loving architecture and history, I had to do three days to see all the main temples and the hidden treasures as well.
For the sake of time here is a brief description from Wikipedia on Angkor Wat:
Angkor Wat (Khmer: អង្គរវត្ត) is a temple complex at Angkor, Cambodia, built for the king Suryavarman II in the early 12th century as his state temple and capital city. As the best-preserved temple at the site, it is the only one to have remained a significant religious centre since its foundation – first Hindu, dedicated to the god Vishnu, then Buddhist. It is the world's largest religious building. The temple is at the top of the high classical style of Khmer architecture. It has become a symbol of Cambodia, appearing on its national flag, and it is the country's prime attraction for visitors. Angkor Wat combines two basic plans of Khmer temple architecture: the temple mountain and the later galleried temple, based on early South Indian Hindu architecture, with key features such as the Jagati. It is designed to represent Mount Meru, home of the devas in Hindu mythology: within a moat and an outer wall 3.6 kilometres (2.2 mi) long are three rectangular galleries, each raised above the next. At the centre of the temple stands a quincunx of towers. Unlike most Angkorian temples, Angkor Wat is oriented to the west; scholars are divided as to the significance of this. The temple is admired for the grandeur and harmony of the architecture, its extensive bas-reliefs, and for the numerous devatas (guardian spirits) adorning its walls.
The modern name, Angkor Wat, means "City Temple"; Angkor is a vernacular form of the word nokor (នគរ), which comes from the Sanskrit word nagar (नगर), Thai, Nakon, meaning capital or city. Wat is the Khmer word which comes from Sanskrit word "Vastu". Prior to this time the temple was known as Preah Pisnulok (Vara Vishnuloka in Sanskrit), after the posthumous title of its founder, Suryavarman II.