According to Wikipedia, the Italian Renaissance era in art lasted from about the late 13th century to the late16th century. This article gives a broad overview of subject matter and influences of the Italian painters. The Catholic Church commissioned many works, particularly large-scale ones, so therefore, religious art flourished during this time. Portrait painting didn't become popular until later in the 15th century. Classical themes were also popular.
But strictly speaking just through observation, here are a few of my personal comments about the art of this period: Proportions are distorted. People's necks or torsos are often very long with huge thighs. Many of the faces have an almost porcelain look and some are downright grotesque probably without meaning to be. Backgrounds are usually unrealistic—in fact, they seem to appear as if the people themselves are standing in front of a painting of a background! Buildings give the impression of being disproportionably small for the people in the painting. Colors tend to be dark, and few outdoor scenes look like a bright sunny day. And that's my opinion!
But the works of this period are still lovely to view and study, and of course, some of our greatest artists came from this period. That includes Michelangelo, Raphael, Titian, Botticelli, and of course, da Vinci. I have not included any of da Vinci's works here, because I have a book and CD-ROM devoted solely to his works. I have chosen a few painting from the collection as representative, but keep in mind, these works may be found in other places on my site, particularly in the Cross-Reference/Resource index.
As always, you may mouse-over any image for more information.
Sandro Botticelli: Young Woman (Simonetta Vespucci?) in Mythological Guise; c.1470-85
Lorenzo Costa: A Concert; c.1485-95