Is the Sigma 150mm f/2.8 EX DG APO HSM Macro Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 300mm f/5.6 test image. Observe the contrast and resolution of these results.
Is the Sigma 150mm f/2.8 EX DG APO HSM Macro Lens set to 300mm f/5.6 sharper than the Tamron SP AF 180mm f/3.5 Di LD IF Macro Lens set to 180mm f/3.5? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.