When we bought our 60D, we thought the 18-55 lens kit was a good deal - and it probably was. But we have been building our collection of lenses, and having supplemented the original lens, we decided that it was already time to replace it with something rather better.
This lens is in a different league, which frankly you would expect given the huge jump in price. It is big, solid, and rather heavy, but it fits on the the camera with a very satisfying clunk, and once there, it feels surprisingly well balanced and not at all unwieldy.
There is one area that this lens does to seem to suffer in according to the reviews I read, and that is vignetting. I had already ensured the camera had the data for this lens installed to allow the built-in peripheral illumination correction (IE: vignetting compensation) to work. If you have a camera that supports this and you have not investigated it, do it. The in-camera correction it does for JPGs is really very good. If you tend to shoot RAW, then you can probably get even better results post-camera in the DPP software. But the in-camera correction is still very good. Take a picture of an evenly lit blank wall without flash, with and without the option turned on, and you can see the results very clearly.
One feature of this lens that I particularly like is that you can operate the manual focus even when the lens is in autofocus mode, and when the camera is focussing, the focus ring does not turn, so you don't have to worry about how you are cradling the lens in your hand while shooting and obstructing its movement, or possibly even breaking it, as you might do with other lenses.
If you are buying this lens and also want a hood for it - don't pay a fortune for the Canon one. Look for JJC - it is less than a third of the price, and is very good quality - fits well and does not obscure any of the frame.
I have seen some reviews which say that there isn't much difference in quality between this and the 18-55. That aside for a moment, this lens does give a lot more at both ends of the scale - 15 is gratifyingly wide-angle, while 85 is a really very decent general purpose zoom. But on the quality front, for me there is no contest. This lens is streets ahead of our 18-55, which suffers quite bad chromatic aberration. Maybe it is faulty, I don't know. But I am very happy with this replacement. It's expensive, and when you look at the results, you can tell.