This lens is one of a pair of very high quality wide-angle "L" lenses introduced by Canon in the late 1990s. (The other is the 35mm f/1.4 L). It offers great contrast and superb background blur, and is Canon's fastest wide-angle lens. Great for big landscapes, and indoor architecture, amongst other things.
It was replaced by the 24mm f/1.4 L Mk II in 2008. That doesn't make this one rubbish - it was, and still is, an excellent lens. (But the Mk II is even better.)