The Canon EF 14mm f/2.8 USM L II is the widest full format lens in the Canon EOS lens lineup. Within its native format it covers a whopping field-of-view of 114 degrees. This is a bit beyond most ultra-wide applications for mainstream users but sometimes there's simply a need for such special effect lenses. The EF 14mm f/2.8 is a rectilinear lens and thus distortion-corrected (as opposed to a non-corrected "fisheye" lens).
The lens features a "bulb-like" front element - such designs became popular (again) recently because it is obvious a superior approach for correcting the rather difficult aberrations (optical defects) ultra-wide lenses have to deal with. As such it is certainly a promising lens.
The build quality of the lens is excellent just as expected from a members of the professional grade Canon L family. The lens body as well as the fixed petal-shaped lens hood are made of metal and there're seals against dust and humidity. The front cap can be slid over the lens hood and it's certainly a good idea to do so during transport because the large front element is naturally quite vulnerable. The focus ring operates smoothly. The physical size of the lens remains constant regardless of the focus setting.
The Canon lens features a fast ring-type USM drive with FTM (full-time manual focusing in single shot AF). This is surely not a critical feature for such a lens but it's appreciated nonetheless (just make sure that you don't waste depth-of-field by focusing towards infinity).