With plenty of impressive technology inside the lens, it comes as little surprise that the lens performs to an exceptional standard. It produces negligible distortion, and next to similar lenses it produces surprisingly little chromatic aberration, too.
Its sharpness throughout the range is likewise hard to fault. At its widest f/2.8 aperture, it boasts a central sharpness that many other macro lenses lenses only match once stopped down, and when it taken down to its middlemost aperture it manages to equal the performance of the Zeiss Makro-Planar T* F2 100mm ZE, which is more than double its price.
Unsurprisingly, things aren't quite as impressive at its f/22 minimum aperture, although images are still usable. Overall, though, if there's room for improvement anywhere here it's with its consistency, since throughout the first half of the aperture range the lens is slightly softer in its edges than it is in its centre.
Overall, Sigma should be very proud of this lens. It's packed full of functionality and it performs to a high standard, and considering its performance it's priced fairly too. If you can get over its size and weight, it's a cracking piece of glass to have.