Resumen: In short, this is clearly a very impressive lens in all respects. It is also keenly priced. Yes, for only about £150 more you could buy Canon’s very capable 24-105mm f/4 zoom, which is a better all-rounder, but the 100mm macro is not meant to be an all-rounder: it has been conceived for one specific...
Conclusión: Just occasionally a lens turns up which delivers such implausibly good results in our studio tests that I have to go back and repeat everything, double checking all settings to make sure I haven't done something wrong.
A favor: Superb optical quality, Fast, silent, and accurate autofocus; full time manual focus, Highly effective image stabilization (for longer subject distances, at least), Solid build, including dust and water sealing
Contras: Hybrid Image Stabilization still not particularly effective at macro distances, Precise manual focus at 'portrait' distances slightly tricky, Very expensive compared to non-stabilized alternatives