I understand this lens is a compromise, it is sharper than the 18-55 and slightly softer than the 50-200 kit zooms. Colour and contrast is below the standard of the 50-200, however it's close enough to justify replacing the two kit zooms with this lens. The sweet spot is between 20 and 100mm where the lens is sharper than it has any right to be. It's also quite tolerant of being used wide open compared to kit zooms.
Weaknesses include very strong distortion at 18mm, abberations near the wide end, muddy colour (not unusual for Tamron consumer/kit lenses), a tendency to ghost if slightly over exposed and strong vignetting throughout the range. This lens exhibits severe shortening of the actual focal length when close focussing, 250mm is equivilent to about 150mm on the DA50-200 at about 6ft.
Overall though, it seems far stronger than previous ultra zooms and at the very least covers the kit zoom range without changing lenses.