Note this will be a work in progress review. This part will be text only. I will add pics later.
The lens was bought as part of kit with the 7D, but is available by itself.
The build quality is good but doesn't make it up to excellent. The lens body is plastic and it feels very solid. Dominating the front half is a generously sized zoom ring. This is forward of a very thin manual focus ring, so the order is reversed from normal. Both rings feel smooth in operation and have a nice amount of resistance. Do note the direction of the zoom ring is typical Canon, which is opposite compared to Sigma/Tamron lenses.
The lens extends when you zoom. The barrel extension is solid and doesn't wobble at all. Currently it does not exhibit any zoom creep even angled straight up or down. Possibly this may change with long term use, but unlikely to be a big problem as the lens isn't that heavy. There is no zoom lock.
The MF ring is quite thin. With your hand under the lens, your thumb will end up on the focus ring next to the IS/MF switches where it feels a little restricted. The focus ring is on a thinner part of the lens body than the generous zoom ring, so it is unlikely you'll nudge it by accident in normal use. It is assumed most people will use this lens with AF, and rarely use MF so this is unlikely to be a big problem.
The lens front does not extend or rotate when focusing so polariser users will not have a problem there.
It is traditional to bash Canon for not including a matching hood on their non-L lenses, and this remains the case here. I did purchase the optional hood too. To their credit, I think the hood build is slightly above average as it includes the black felt material lining to prevent reflections from the hood itself. Being a wide angle lens, the coverage provided by the hood isn't much, and is configured in a petal arrangement. The shading advantage from the hood will be minimal at longer focal lengths, but it still provides some protection of the lens front. The hood can be reversed for storage on the lens.
Looking thought the viewfinder, the IS seem to be effective. With only practical use observations and not controlled measurements, it does work effectively as expected.
USM works fast, and AF just snaps in place quickly. Compare this to the conventional motor driven Tamron 18-270 which nibbles its way to the right point.
Resolution is no problem with this lens. I have confidence to use it from wide open. It does exhibit some distortion most noticeable at the wide end, but this is typical for the lens zoom range so they're within expectations there. It isn't a fast lens at f/3.5 on the wide end, going up to f/5.6 on the long end. So far I haven't noticed any significant CA with it.
Overall, this lens should be considered if you want a premium standard zoom lens for EF-S compatible Canon bodies. The 15mm at the wide end is the widest Canon do without going for a dedicated wide angle lens, and at this point it does make a difference compared to more typical 17 or 18mm lenses.
Other Canon lenses to consider may include:
EF-S 17-55 f/2.8 IS USM - this trades off the zoom range at both the wide and long ends but gains you a constant f/2.8 aperture. If you prioritise aperture over zoom range, this is one to look at.
EF-S 17-85 IS USM - the predecessor to the 15-85, it is quite a bit cheaper.
_________________Canon DSLRs: 7D2, 7D1, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 85/1.8, 135/2+SF, 70-300L, 100-400L, 100L, MP-E 65, EF-S 10-18, 15-85
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 50/1.4A, 150 macro, 120-300 f/2.8 OS
Compacts: Sony HX9V, Fuji X100.