Conclusion: I purchased this lens for shooting small black box theatre productions without a flash, and these venues are typically not well lighted. This worked wonderfully with my Rebel. When I upgraded to a 5D and a 5D MkII I found this lens to be lacking. It still functions wonderfully, however the very pronounced distortion with the full frame boxes creates a poor fish-eye effect. Considering the investment required, it is an unforgivable drawback.
Pros: Fast auto-focus, Superior build quality, Super-sharp images
Summary: This last copy of the 24mm was the last straw. I kept getting soft images on all three copies...I tested the auto focus and it was off just as in the last two copies and required micro-adjustment. Even using manual focus produced less than great results for such an expensive lens. No matter what aperture I used from 1.4- f/16 it was soft in the center and worse at the edges. There are some good copies out there as I have read the reviews.
Conclusion: I have wanted this lens for a long time and finally ordered it. I just received this lens today. I have taken about 100 photos using my 7D using various focus points. Only about one third of these did the auto focus work. It's getting returned.
Conclusion: Build quality is high as expected for this lens. However the focus is inconsistent and the lens has severe front focus around 1.8. I owned the mark I predecessor and loved it, so when it was stolen I immediately replaced it with this one. Today I am returning the fourth copy in an attempt to get a good one. I thought it was a bad batch or simply bad quality control, but now I believe it is a design flaw.
Summary: I'm on my 3rd Canon 24mm f1.4 L version II, all have had focus issues. The 1st was crazy inconsistent. The 2nd had a huge front focus and was still somewhat inconsistent. The 3rd that I just received is also inconsistent. I've tested the lenses on many different camera bodies and in many different situations. I've even had a Canon engineer confirm the inconsistency issues on the 2nd lens (he recommended I return it for a replacement).