Just a quick side-by-side comparison with what I had been shooting with (extension tubes on a 70-300).... this lens by itself is pretty much equal to that. But, add the extension tubes to the 105, and you get this stuff.
Plus, it's an FX lens, so when I go to an FX body, it won't need to be replaced. Plus, it's f/2.8.... fairly bright in the VF. Plus it's the same size as my set of tube. Plus it's sharper than my old set-up.