However, you have to say, there is no L Canon lens and thus it must have these limitations.
I love to take pictures with it, if only when I think of the purchase price.
It's definitely better than the processed Tamron SP AF 17-50mm Di II VC lens 2.8.
The autofocus is due to HSM engine also afloat. The Tamron is as very slow.
The accuracy of the AF is super, at least in my constellation EOS60D and Sigma EX.
The sharpest and best results get with 25mm aperture and 4 or 5.6.
Aperture 2.8 you should only take if there is too little light.