From the World Heritage inscription:
Copán with its temples, plazas and terraces, comprises a type of architectural complex among the most characteristic of the Mayan civilization. The lengthy inscription on the Hieroglyphic Stairway Plaza is of considerable historical significance
The Mayan city of Copán as it exists today is composed of a main complex of ruins with several secondary complexes encircling it. The main complex consists of the Acropolis and important plazas. Among the five plazas are the Ceremonial Plaza, with an impressive stadium opening onto a mound with numerous richly sculptured monoliths and altars; the Hieroglyphic Stairway Plaza, with a monumental stairway at its eastern end that is one of the outstanding structures of Mayan culture. On the risers of this 100 m wide stairway are more than 1,800 individual glyphs which constitute the longest known Mayan inscription. The Easter Plaza rises a considerable height above the valley floor. On its western side is a stairway sculptured with figures of jaguars originally inlaid with black obsidian.
From what is known today, the sculpture of Copán appears to have attained a high degree of perfection. The Acropolis, a magnificent architectural complex, appears today as a large mass of rubble which came about through successive additions of pyramids, terraces and temples. The world’s largest archaeological cut runs through the Acropolis. In the walls of the cut, it is possible to distinguish floor levels of previous plazas and covered water outlets.
Copan is undoubtedly one of the most significant Mayan sites in Mesoamerica and most important cultural site in all of Honduras.
While not as large as other Mayan sites such as Tikal, it is reasonably large in its own right and also has one of the best collections of Mayan stelae in the world. The quality and detail which can still be seen in the stones can be found in few other places.
The site is situated only 15 km from the Guatemalan border which makes it easy to visit if you are visiting other sites in the region. Tours and transportation can easily be had from the city of Copan Ruinas.
Given the size of the site, you might want to dedicate 3-4 hours to explore the ruins. There is also a museum on site which can be entered for an additional fee.
View the complete list of UNESCO World Heritage Sites that I have visited.