Sigma 18-200mm F3.5-6.3 DC OS HSM is an Auto Focus (AF) SuperZoom lens with APS-C / DX max sensor coverage. When mounted on a APS-C / DX sensor camera, it will give you an FF equivalent focal range of 27 - 300mm. With a max aperture of f3.5 at 18mm, we can not consider this lens fast on wide end, and it is slow at the tele end with its max aperture of f6.3.
This lens features on optical image stabilization which helps capturing sharper images at lower shutter speeds. Sigma 18-200mm F3.5-6.3 DC OS HSM is not a weather sealed lens, so you have to be extra careful against rain and dust. Sigma 18-200mm F3.5-6.3 DC OS HSM was replaced with Sigma 18-200mm f3.5-6.3 II DC OS HSM Nikon F DX. Follow the link to read our comparison of these cameras:
Compare Sigma 18-200mm F3.5-6.3 DC OS HSM Nikon F DX vs Sigma 18-200mm f3.5-6.3 II DC OS HSM Nikon F DX