Is this tree a square peg in a round hole? An ugly sister in Cinderella's slipper? Do the trunk and branches of this tree lend themselves better to a different style or different planting angle? Slanting, cascade, literati? Trees can adapt to different styles over time or with heavy manipulation but they are more likely to be successful if they naturally fit the chosen style.
Is there a pleasing taper in the trunk from fat to thin? (Though slender trunks are sometimes okay!) Does the trunk have movement, curves or angles that tell an interesting story? (Formal uprights are exempt!) Is the line of the trunk beautiful?
Where the trunk meets the soil, is there a pleasing and natural-looking spread of surface roots? Do the roots match the style and angle of the tree?
Most bonsai have one distinctive branch that is more noticable and more important in the design than all the other branches. Does this main branch look good? If there is a second branch which is almost as noticable as the first branch, consider both branches.
Bonsai are usually representations of mature old trees, even though the plant material itself may be relatively young. Does the bonsai appear old? (unless the Bonsai is obviously meant to represent a youthful tree!)
Does the tree look good in this pot? Would it look better in a different size or style of pot?
How refined are the twigs and foliage? Do the branches divide and subdivide into fine twigs, making the tree look much bigger than it is? If there are leaves or needles, do these look uniform and appropriately sized (preferably small)?
Notice the silhouette of the tree, does this have a pleasing shape?
How much do you like the bark on the trunk? It may be rough or smooth, still it should add to the character and story of the tree. Any scars should look natural rather than artificial.
If there is deadwood exposed on the trunk or branches, do you like the look of this deadwood? Does it add to the character of the tree and look natural?
If there is no deadwood, simply leave the slider at zero.
Does the tree look healthy to you?
Does the tree seem stable? Does it look heavier on one side, as if it's about to fall over? Are forces counterbalanced?
As you contemplate the tree, notice how your eye moves around the design, does it flow around and around in a mesmerising way like a model train on a track, or does it get derailed at some awkward jarring point?
Is your eye drawn to particular areas of the bonsai? Are those areas sufficiently more detailed and interesting than the rest of the tree? Is there a dynamic difference between the focal points and the other, more background, nondescript areas of the bonsai image?
Are dense busy areas of foliage nicely contrasted by open areas of negative space? Is there a pleasing rhythm to the spaces?
Is there order in the tree or is it too chaotic? Do the branches share a similar shape and character? Are there repeated motifs in the lines and angles? Is the tree self-similar like a fractal?
Has everything unnecessary to the design been removed? The opposite of realism, expressing more with less.
Is this tree one in a million, would you recognise it if you saw it again? Would you want to come back and look at it again and again? Does the tree speak to you, can you relate to it like an old friend? Does it achieve excellence in a way that transcends rules and guidelines?