Hilleary "is best known for his commitment to creating harmonious, expertly executed canvases in variations of a signature style." His signature style revolved around his "interest[] in patterns as well as colors—patterns not simply as decorative displays of color, but as on intricate arrangement of what the Futurists called lines of force." Despite the centrality of lines and angles to his work, though, Hilleary has been described as a Lyrical Abstractionist artist. That description may reflect the evolution of his art. Washington Post art critic Benjamin Forgey observed that Hilleary "at first adopted the then-reigning hard-edge format utilizing relatively subdued optical color combinations" but over time his work evolved to show a "gradual release of lyrical energies, in which softer colors and thin, translucent overlays of paint have been added to the logical structure of interlocking vertical and diagonal stripes."Washington Post: "James Hilleary" by Benjamin Forgey (February 12, 1978)
