A good one usually has a compelling plot with unexpected twists. The characters should be well-developed and their motives clear. Also, a sense of tension and mystery keeps readers engaged.
A good small crime short story often has a unique setting. The crime should be logical yet intriguing. The pacing is important too - not too slow or too fast. And a touch of moral ambiguity can add depth.
For a great small crime short story, you need a strong hook at the beginning to draw readers in. A clear resolution that makes sense is essential. And don't forget about vivid descriptions to set the scene.