With Joan Mitchell gone some 15 years, her work exists in that tender territory where artcritical response shades gradually into art-historical assessment. At her best, the Chicago-born Abstract Expressionist was indisputably great, painting her unironic emotional response to the landscape with a focus and ferocity that conveys ecstasy.

A few of the pastels in “Joan Mitchell: Works on Paper 1956–1992,” on view at Cheim & Read, equal that achievement. But overall, Ms. Mitchell’s legacy is not well-served by the show. As this exhibit makes clear, focus can be fleeting, and ferocity elusive; included here is an admixture of second-rate work. Fortunately for her fans, the interesting failures outnumber the uninteresting ones.

The show unfolds in roughly chronological order, starting, in the gallery’s front room, with five smallish oil-on-paper pieces from the late 1950s, just prior to Mitchell’s move to Paris from New York. One of these, “Untitled” (1956), really sings. Its raspy, darting calligraphy of ochre and green, hot bits of red and orange, and a throbbing cobalt blue is reconciled to the sheet by means of broad swatches of near-white. The others look half-baked in comparison.

Color is so essential to Mitchell’s oeuvre that it is a surprise to see two untitled charcoal drawings from 1967. They are in rough shape, but unusual in their use of the eraser to selectively repopulate the shadowy, tumbleweed figure with the white of the ground. A pair of 30-inch-by-22-inch works, in ink, gouache, and pastel, don’t quite take off. Nonetheless, their play of warm and cool grays is masterful, and their calculated juxtaposition of agitated scribbling and drifting, gently modulated areas has much in common compositionally with Mitchell’s Japanese-screenlike paintings of the period.

The best works in the show are pastels, a medium for which Mitchell had an obvious affinity. Several, such as “Tilleul” (1977) and “Untitled” (1983), both 23 inches by 15 inches, are done in by relentless smudging, which suffocates the paper. But in her final years, the artist’s finesse became truly astounding. In this generally overhung show, the full-immersion strategy works splendidly in the gallery’s back space. It houses nine expansive 48-inch-by-32-inch pastels from 1991. Here she is at her most playful. One piece hinges on crisp, whiplash strokes of cherry red and manganese blue that are smudged just enough to pull the pigmented powder into a translucent, grapey membrane.

Two others hanging side-by-side make plain just how tricky this game is. They share a volcanic palette and an impatient, febrile touch. From “Pastel” emerges a glimmer of structure, as underlying lemon yellow, umbers, and oranges counter slashing strokes of black, red, and pungent blue. It is delightfully inchoate, but still suggests immanence; the adjacent “Untitled” remains a bleary blob.

Many of these works daringly depart from the compositional typology Mitchell favored. That vocabulary is in full flower in “Joan Mitchell: the Last Prints,” at Susan Sheehan Gallery’s new Chelsea space. The largest of these lithographs, “Trees” I through IV, were made with Ken Tyler at Tyler Graphics in the fall of 1992. In each, five bundles of hammering vertical strokes, anchored by black and embellished with snaggles of buttery yellow, orange, and magenta, march across a 57-inch-by-82-inch expanse of paper. In the smaller “Champs” series (1991–92), published in Paris by Atelier Bordas, the image is turned on its side, and the bundles become a field that retreats in spatial leaps to a sketchier, uppermost stratum — the sky. They are elemental, taming the landscape into modular units even while hinting that underneath the cultivation, dark forces rage.

Lithography suited Mitchell well. In a manner different from her late pastels, she wrings maximum punch from just a few colors through the blending of overlaid inks. She revisits familiar motifs, consistent with the adage that the function of printmaking is not to discover an image, but to express a preconceived one. The ribbony flutter of two “Sunflowers” (1992) distills the gloriously discombobulated, allover canvases that had occupied the artist since at least the mid-1980s. The verdict of time may well be that, in their chromatic cohesion and clarity of intent, these prints are an improvement.

Cheim & Read until June 16 (547 W. 25th St., between Tenth and Eleventh avenues, 212-242-7737); Susan Sheehan Gallery until July 28 (535 W. 22nd St., between Tenth and Eleventh avenues, 212-489-3331).