I have 24f1.4L but still got this little "ugly duckling". I need a compact 24mm prime on 5D. I compare it to 24L. The border and corner sharpness is better than 24L!. Center falls short to 24L which is expected. IMO, from f2.8 and above, 24L is about equal to 24f2.8. 24f2.8 also has very low distortion, seems better than 24L. However, 24L has better color, contrast and silky boken. I know it' not fair to compare it to 4 time priced lens. What I want to say is if you don't need f1.4~f2.8, 24f2.8 is obviously better buy.
This little guy makes me think whether I should keep 24L. It looks like 24L is only useful for extreme low light or better boken. No much strength in other situation.