Is the Canon EF 28mm f/2.8 Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 28mm f/11.0 test image. Observe the contrast and resolution of these results.
Is the Canon EF 28mm f/2.8 Lens set to 28mm f/11.0 sharper than the Canon EF-S 18-55mm f/3.5-5.6 IS Lens set to 28mm f/11.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.