Antonyms for the phrase "how things stack up" can include "disorderly," "chaotic," "confused," "random," "jumbled," and "unsystematic." These antonyms all indicate a lack of organization and structure, suggesting that the situation in question is difficult to comprehend or make sense of. On the other hand, "orderly," "structured," "systematic," and "well-organized" are antonyms that suggest a clear and logical arrangement of things. When things are seen to stack up well, it indicates that there is an underlying coherence or pattern that can be discerned. Conversely, when things do not stack up well, it suggests a lack of clarity or direction.