Well, if you know what you're looking at here, then you know that you want it. This is Canon's Holy Grail of macro lenses. It's the lens of choice for nature macros, for two very important reasons:
If you're looking for a great general purpose lens that also does 1:1 macro, you might want to consider one of Canon's two 100mm macro lenses: the 100mm f/2.8 Macro or its grown-up sibling the 100mm f/2.8 L Macro IS. They're both less expensive, they focus more quickly, has similar image sharpness and have a more generally useful focal length. But if you're specifically after great nature macro photos, then you've come to the right place.