Its fine, but not as useful or as sharp as my 24-105mmL for all around use. Where it comes in handy is in low light, or for a shallow depth of field.
If you a new 5D MK III user, give it a while with the 24-105, you will get used to the weight. Good lenses are heavier due to the large amount of glass in them. The 24-105 is on the light side compared to the 24-70 f/2.8 or some of the other popular "L" lenses.