It should be VERY sharp in most situations where L zooms would normally be sharp, that is, with the right lighting, aperture, etc. (Of course if you shoot primarily with the ef 70-200mm f/2.8 IS II, or, from what I've heard, the new 24-70mm, you might be spoiled...) The 24-105mm is a fine little workhorse, sort of a Swiss Army knife kind of lens.
I have one that was really bugging me because mine seemed to be way underperforming compared to ones owned by two other photographers with the same combo, the 5DIII and the 24-105. A bad run of shots at an event finally prodded me to send it (under warranty) to Canon, and it came back as if it were an altogether different lens, just outstanding sharpness and all around IQ. Now I love it.
Canon reported that they swapped out a circuit board, and because the work was done so quickly, I have the feeling this is not a rare problem, but one they knew about based on my description.
One other thing: If you LOVE your camera, and you got it as part of a kit, I would strongly recommend keeping the camera that works great, but send the lens to Canon for repair. I've had the frustrating experience of having one part of a kit just perfect, sending back the whole thing because the other part was questionable, and then ending up with a new set of problems.
In fact, in the future, I'd probably pass on the kit savings to make separate purchases of camera and lens, just so I don't have to worry about this scenario again.