Is you need super-low DOF in your wides, no.
Wide open, f/2.8 at 24mm I expect a lens this expensive to have abolutly no vignetting.I don't know if you get over it...but you learn to live with it BECAUSE the lens is SO sharp and REALLY has great fit & finish. Feels incredible in the hands, (and I cannot believe that I am saying that about a zoom). I never felt that way about my 24-105.
But then after a bit I get over it. Dylan777 is correct it does have vignetting. As he said as long as it is equal you should be ok.
The vignetting and a few other reasons help answer the question, can I replace my 24mm or 35mm L's with this lens.
I was torn...but ended up going for the versatile zoom instead of buying the Sigma 35mm and the Canon 24mm L, (same money being spent). Definitely a TOUGH choice.
Well yes my need may be a super-low DOF in my wides. Not what I was referring to though.
But, there are other things to. Such as distortion.
ah...you are correct...there are issues there as well. Just was not that important to me..If you look at my lens quiver, I have a lot of good glass...and I just had to make a decision for me...do I always want to be carrying and switching prime lenses out. I decided that sometimes I want to grab my camera, (I got a small holster bag just for this lens on the camera), run out the door, be light footed, have versatility and know that I can come back with the "good" goods. The 5DIII and the new 24-70mm do allow me to truly do that, with (for me), very mild compromises. (when I need shallow DOF I am going to my 50mm Sigma or my Canon 85mm L, anyway).
I think that became my priority, and it ads versatility to my kit, for me. I want it all and just don't have the money or a packmule who can hold reflectors for me either!!!!
My next purchase will definitely be the Zeiss 15mm, f/2.8 ZE. I am gaining strength were I can. We all have to find our way as to what is important to our photographic journey. Everyone should have a good ride!!!!!