A few first thoughts...,
The Body and 24-80 2.8 lens have a magnificent feel, metal. The lens body and ring grips are aluminum, no rubber. The inner lens barrel and lip is plastic/carbon fiber, like Nikon. I like the absence of the rubber rings as the dust attraction drove me nuts. The body is just a little tank, mag alloy. The body is probably about 25% smaller than a Nikon Dx body. The pro 24-80 2.8 is about 60% the size of the tamron 24-70 2.8. Exterior controls are great, there will be no menu surfing while shooting!
Cons so far:
The battery charger is corded, another thing to pack. The LCD must be pulled down to open the USB plug for uploading. Very minor things so far. There is some frustration in learning new controls from a different manufacturer, but it's not oly's fault.