The size and weight is really appealing to me.
One feature that is easy to overlook is the minimum focus distance of 20cm, which is the same as the EF14mm f2.8 L. When shooting wide, going very close to your subject can make the image much more interesting (fill the frame). The difference in perspective you get with a wide angle lens makes is tempting to photograph smaller subjects, like flowers, while still getting nice bokeh, and include an interesting background . That is the feature I love the most with the EF 14mm. I also own the Zeiss 15mm f2.8 classic, and I find the Zeiss much harder to use because of a poorer minimum focus distance, which is making it harder to fill the frame with my desired subject, and harder to get pleasing bokeh.