I have been using the 24mm for the past few months and it is by far the highest quality wide angle I’ve had the fortune of using.
Photographing through the aperture range vignetting remains low, and the sharpness at f/5.6-f/8 is incredible. Pairing this with the Canon 5D Mark II really takes advantage of the full frame sensor and produces truly incredibly resolution.
Build quality is the same as the other Art range lenses, I’ve been using and that is superb. The all black design keeps the lens very discreet. It is however quite large and heavy, so all together it does mean lugging around 1.5kg.
Being a prime, quality does come at a trade of with convenience. I do enjoy having a zoom for quickly changing composition, like the 24-70mm f/2.8, but that has a much lower image quality and overall sharpness.
I can’t recommend this lens enough, if your a landscape photographer this is a serious lens to consider.