I have what I believe is optically the same lens, the Sony DT 18-200mm f/3.5-6.3 Aspherical ED High Magnification Zoom Lens for Sony Alpha Digital SLR Camera but in a Sony lens mount, which may be slightly better quality than the Tamron lens mount (Sony apparently owns Tamron, and several Minolta and Sony SLR zoom lenses have Tamron optics in a Minolta or Sony lens mount; one such is the Minolta 28-75mm f/2.8, another is the Sony 18-250mm f/3.5-6.3). Since the Sony mount lenses cost only about $50 more than the similar Tamron lenses, readers may want to compare them. Some reviews that I have read say that the Sony mount lenses have faster focussing. Mine has very fast autofocus.
My Sony 18-200mm lens is mounted almost permanently on my Sony Alpha 700 body, and I agree that it is sharp as a tack. The first test photo I made was a full-body photo of my cat, and you can almost count the individual hairs in his fur - needless to say, every whisker is sharp. Admittedly, the lens was set near its 'sweet spot' at f/9.5 at 70mm focal length. It could hardly be any sharper.
As for build quality, the zoom is well damped, there is no zoom creep, focussing is fast and accurate. I am very pleased with this lens.