The Canon 8-15mm F4 L is a unique lens for the unbelievable angle of view and crazy distortion it produces.. It is perfect for being creative and a must for photographers that want to shoot spherical panoramics. The reason why it is so successful for panoramics is that you reduce the amount of photographs you will need to take. The less photographs taken between shots for example on a windy day can determine if the sky and clouds will match up. On the 15mm index you can take 8 photographs in a 360 degree turn which comes in very handy.
Overall it can be a fun lens when taking photo's of friends and make their face look funny.
Price wise it is not cheap.