For those who don't know, the Pentax DA 18-250 is a rebadged version of a Tamron lens. The Tamron represented a big leap in design and quality in super-zoom lenses over the earlier 28-300 and 18-200 models.
The Pentax-badged version has the advantage of working with in-camera jpg correction on more recent Pentax DSLRs.
I've had the Tamron-badged version since 2007. It was my only lens for 6 years. It's versatility is its main virtue, but centre sharpness and colour rendering are also surprisingly good. It's at its best at the wider end, particularly from about 24-70mm. Minimum focus distance is 45cm (about 18"), so it's good for close shots. I actually prefer this lens to the 55-300 at its wide end (say about 55-85), because sharpness is similar and I like the colours better.
It's slow of course - about a stop slower than the 55-300 for example through most of their common range. Widest apertures are:
18-34mm f3.5
35-49 f4
50-69 f4.5
70-99 f5
100-199 f5.6
200-250 f6.3
Given that (like most zooms) it's best stopped down by a stop or two, it's obvious that this is a lens for good light, especially at the long end.
Of course there is a lot of distortion at the wide end. That might bother some people, but not me: it's easily corrected in PP. The automatic correction in DxO Optics Pro does wonders.
My copy also has zoom creep (it doesn't bother me). As Dewman says, construction is generally very good. After 7 years of use, mine has no barrel wobble or other problem.
Now I have a range of other lenses, the 18-250 has been relegated to use as a travel lens or where carrying other lenses or changing lenses is a problem. It does that role very well.
I would also recommend either the Tamron or Pentax 18-250 as an alternative to the 18-55 and 50-200 kit lens combo. Only slightly more weight than either of those lenses, and less than the two combined, image quality is better, maximum aperture is about the same and no need to change lenses. The only disadvantage is the lack of the weather-resistance provided by the later versions of the kit lenses.
Here are some examples from the Tamron 18-250. The first, fourth and fifth are OOC jpgs taken with my old K100D Super. The second and third were shot in RAW with the K-30 and PP'd a little. They aren't put forward as technically stellar, just as examples of the versatility, and the sort of results available in ordinary use.