I am a member of the waiting-for-the-24-Art-Lens club. I have been very anxious to see what level of performance this lens would turn in. Though the chart used in the image quality test is tough on a lens' performance, it mirrors what I am seeing in real world results. While I am not amazed by this lens' wide open performance, it is at least as good as the FAR-more-expensive Canon 24mm f/1.4L II and it is razor sharp when stopped down slightly.
Here are some comparisons:
Sigma 24mm f/1.4 Art vs. Canon 24mm f/1.4L II Lens
Sigma 24mm f/1.4 Art vs. Canon 24mm f/2.8 IS Lens
Sigma 24mm f/1.4 Art vs. EF-S Canon 24mm f/2.8 STM Lens
Sigma 24mm f/1.4 Art vs. Nikon 24mm f/1.4G Lens (different camera systems)
Sigma 24mm f/1.4 Art vs. Sigma 24mm f/1.4 EX Lens
I hope to have this full review completed in the next week or so. Stay tuned.