Is the Sigma 18-200mm f/3.5-6.3 DC OS Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 100mm f/11.0 test image. Observe the contrast and resolution of these results.
Is the Sigma 18-200mm f/3.5-6.3 DC OS Lens set to 100mm f/11.0 sharper than the Canon EF 50mm f/1.4 USM Lens set to 50mm f/1.4? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.