I bought this lens recently to replace an old sigma telezoom and the Tamron 70-300mm Di LD.
This Pentax outperforms both, and even if pricier, I think is a better telephoto.
If you must have "macro" capabilities, then go with Sigma's or Tamron's flavors of the 70-300mm.
I find this lens quite sharp throughout, has great colours (Pentax style) and does not show chromatic aberration problems like the Tamron did.
One of the best points in this lens is the focal range. You'll change lenses less often, and miss less shots. Sadly the minimum focusing distance is a bit to long, if they made it 0.5m shorter it would make a big difference for the 55mm end, in my experience.
In terms of design and build, its the same as the kit lens, its fine for this price point. It has the little window in the shade to change the setting on your polariser filter (great idea Pentax!).
The aperture is not super fast (not surprising for a consumer grade lens) but its not that slow either, I find quite good in the field.What is not that great is the noisy autofocus and slowish autofocus. Its not a big issue, but when shooting birds it can disturb them...
All around I'd say its the telezoom to get.