When hiring an architect and judging his work think about how it relates to other examples of great architecture, such as the Taj Mahal, Chichen Itza, Brunelleschi's Cathedral, the Empire State Building, etc. These buildings are some of the most famous in the world because of how they evolved from their predecessors and how they relate to their environment. A great architect understands both how far architecture has come since the pyramids, and how much he owes to them.
The architect is in charge of macro and micro details, from the way the facade of a building fits into the rest of the urban landscape to the furniture used within the space. All buildings should follow three precepts delivered by Vitruvius, an Ancient Roman who lived in the first century BCE and one of the first who wrote about architecture. In his De Architectura he said that beauty, utility and durability are of primary importance for any building. Hundreds of years later, Leon Battista Alberti suggested that beauty relates directly to proportion, and that ornament can relate too. By the 19th century, Louis Sullivan, father of the skyscraper, said rather simply that "Form follows function."
Architecture is one of the only art forms that is aesthetic and functional. Like when you step foot into the Parthenon, not only are you struck by its ancient beauty, but you can imagine that within its walls of simplicity and strength there were once huge statues of gods and goddesses painted bright colors, with succulent animals sliced open at their feet. The stoic nature of these old columns mirrored the balanced devout nature of its devotees.
Today architecture works in a similar manner, except it has a few more resources up its sleeve. Take lounge design, for example. When a restaurant designer wants to show his client what he's worth, he incorporates different luxurious elements-silk, velvet, leather, marble, taffeta - which will convey to the lounge's patrons what kind of place they're in. If he's designing a home in the contemporary style, he may repudiate a wide variety of elements and textures for one or two simple minimalist ones, such as wood and glass.
Ultimately, an architect is an artist and his ability to work within constraints of functionality and many different mediums makes his profession quite different from that of a painter, sculptor, writer or musician. That's why when choosing an architect, it's important to examine his other work.