Crit

Dominating Traits:
Line: the entire image is expressed through prominent lines, strokes, parallel lines. (There are virtually no simple, clean shapes of constant color.)
Character of Line: curving, swaying, undulating lines dominate. Circles continue the curves.
Texture: both visual texture/raggedness and physical texture in the paint are prominent throughout.
Color: Blue dominates; Yellow is subordinate.
Value: Dark dominates. light values are subordinate (and there are very, very few mid-values.)
Shapes: Most are swaying, curving, undulating, organic shapes that culminate in spirals and repeated circles in the sky. (only the geometric shapes of the town contrast)
3D Space: Depth is orgaized into several distinct layers or planes -- the foreground cypress tree, the town, the hills, then the sky. Its an oddly shallow depth that makes the animated star-motion seem very near...hardly behind the mountains at all.
2D Space/ Picture Plane: The visual field is divided into three distinct areas: the upper 2/3 is the sky; the lower 1/3 is earth, town, mountains. To the left is a tall, vertical, flame-like form (a cypress tree) that connects earth and sky...almost reaching up from ground to sky.
Direction: the emphasis is on horizontal motion and edges — the landscape, particularly the hills/horizon sway left-to-right while the sky also, tends to move from left to right, leading to the large spirals near the center. (In contrast, the cypress tree dramatically thrusts upward)
Contrast: rather bold, crisp contrasts of value and of hue (blue and yellow) dominate. (there are only a few areas of genuinely smooth/calm contrasts, though the level of contrast within diffeent areas of the composition does vary.)
Quality of Energy/Dynamism/Motion: the compostion is overwhelmingly active, moving and flowing.The linearity and the rhythms of the strokes, and the pattern of waves/lins within the cypress tree, the layers of lines within the stars and spiral in the sky, all amplify the this sense of motion. In contrast, the town below sleeps still and quiet, seemingly oblivious to creation's ongoing activity and mystery — the town, a collection of rigid, geometric, manmade forms, is nestled within the dynamic and utterly alive environment. (which, frankly, brings us to Van Gogh's message)

(look for elements and traits that repeatedly appear)
Unified mainly by consistently prominent texture, rich color and dynamic line qualities.
Pervasive curvilinear, swirling, flowing, spiraling lines fill the sky — these curves unify entire composition and dominate all lines, shapes and contours.  These lines create a sense of movement and flow that unifies the whole, and move the eye throughout the entire work.
The curves, and other lines, tend to move horizontally — the dominating horizontal movement unifies the forms with the frame (the visual field).
There is a heavy texture throughout the painting — both the thick, impasto paint and the fragmented, unmixed colors create a kind of rough, energetic texture the unifies and enlivens the image.
Textures are rendered, mainly by short, definite brush-strokes that trowel through the heavy paint.
The picture plane is divided into two major areas — the sky and the landscape — each has its own quality of line and color.  These two areas are bridged, or connected by a few vertical features that cross the dividing line between sky and earth.  (notably the large tree and the small steeple)
The painting is unified by a limited palette of color — mainly blue-violets (BBV) dominate,  mingled with deep blue-green (BBG), contrasting with yellow-golds (YYO). 
The image is predominantly dark — the low key helps unifies the whole.

(look for alignments, structures or groupings that organize parts into larger entities (gestalt))

(look for contrast of any and every kind. Look especially for similar forms that are varied in some way. Look for anomalies — patterns or norms that are broken.)

The painting is enlivened by some of its most dominating traits, as well as by anomalies that contrast with the norm.
Dominating traits that both unify and provide variety include the very rich, saturated color, the frequent juxtaposition of very dark and very light colors (predominant strong contrasts), the frequent juxtaposition of near-complementary colors/hues (blue-violet and yellow-gold), the heavy impasto texture and the constantly moving lines — all of these are dominating traits, but each is energetic and rich in contrast.

Anomalies include the few prominent, and important, vertical elements — the great cypress trees on the left and the church steeple, particularly. 
There are few geometric shapes among the flowing, swirling lines — the town itself is rendered with geometric, rather rigid buildings.
The golden color is subordinate to the deep blue-violet, but quite powerful because of its scarcity.
The sky has intense areas of brilliant, high-valued yellow and white, contrasting with the dominating dark-valued, deep blues. 

Variety Within Forms/Traits:
The heavy textures vary in pattern from region to region — the sky differing from the landscape, the town differing from the landscape, the tall cypress tree having its own vertical, wavy pattern and texture.
The curves themselves vary a good bit — the wave/flame edges of the cypres tree differs from the undulating lumps of the mountain/horizon, which is different still from the smooth spiral forms in the sky, or the smooth, regular curves of the circles.
The brush strokes (short lines) vary in length, direction, curvature and depth (in thick paint).
Space: varied depth is established mainly through overlapping elements.

Star and moon areas offer intense light/yellow areas contrasting with the dominating dark/blue. These focal areas are heightened, also, by patterns of concentric circles of radiating light around the moon and stars.
The central spiraling region might be considered, as well as the crescent moon in the upper right.

The tall flame-like cypress tree on the left offers a bold vertical form within the flowing horizontals that dominate.

The town, below center-right is a kind focal area — more subued in its color/value contrasts, but distinctly different because of is geomeric, blocky shapes.

Each region of the composition has its own active, focal areas: from left to right, the left 1/3 has the flame/cypress tree, the center 1/3 has the prominent spiraling forms; the right 1/3 has the crescent moon. from top-to-bottom, the active sky, particularly the spiraling form echoes the town below.

While van Gogh's entire composition is active (contrasting lines, shapes, texure) there are relief areas that are relatively dark and have little contrasting light accents.

The foreground is certainly subdued comparted to the sky. Even the uppert areas of the sky is relatively calm with more background/blue than elsewhere and only scattered circles/stars rather than rolling spiral motions.