The K-S1 and the 18-135 lens

Well, as I already wrote in another thread, I think the DA 18-135 is a very good lens optimized for hiking and going light, with a very large focal range from true wide angle to true tele in a very compact and rugged WR package.

Like most modern compact lenses, it is designed to be used with software corrections of aberrations, either in-camera by enabling them on the jpeg engine, or in PP by using the lens profile.

IMO, these software corrections are one of the major improvements of digital photography, and some old-fashioned testers need to understand that most entry level zoom lenses are not designed to deliver uncorrected images.

Da 18-135 is a "Jack of all trades". There are better specialized lenses, which will deliver more sharpness, or have a larger aperture for low light, action or more bokeh, but it offers a unique blend of range, size and handling convenience.

This allows you, when shooting stills, to go with that only one lens and use your DSLR like a high end bridge camera, for instance the Sony RX10, and get comparable low light performance and subject separation, the larger sensor compensating for the smaller aperture.

Thus I think that those who understand it and use the lens for what it has been designed will truly enjoy it.

DA 17-70 and DA 16-85 are larger lenses, with much more glass, thus it is no no wonder that they deliver a better IQ.

They also are more expensive, and the newer DA 16-85 benefits of improved technology in computer designed lenses.

But, with software corrections, DA 18-135 delivers very good IQ stopped down between 24 and 70, and acceptable IQ stopped down at both end, 18 to 24 and 85 to 135.

The 85 to 135 range is very useful for many of us.

Going out with the DA 16-85 or 17-70, you need to take another lens to cover this range.

A DA 55-300 (whether the "old" screwdriven AF or the new PLM)  for instance will be sharper and have less aberrations and a longer range, but it is another big lens to add to your bag, and you will need to change lenses in action, which both can be an issue in some situations.