It's clearly a well built, silent and very easy to use lens

Some very early first impressions: Very solid, well-built lens.

Extremely sharp and well built

Other good features is the very clean design aesthetic (unlike the messy Canon and Nikon lenses), the solid build quality (mix of metal and high quality polycarbonate plastic in the exterior and supposedly inside as well), the same 82mm filter thread like the 16-35 GM, the focus lock button that can be reprogrammed for a certain number of other functions (not as many as a regular function or programmable button though), the AF/MF toggle switch, and the zoom lock button (only at 24mm).