David also has a review of the Sony A7. I think it's cool that he is not afraid to talk about pro equipment on his new Yahoo Tech site. (I wish him luck with it. I've been reading him since 1995, and he is tops in popularizing tech.)
It seems reviewers agree that:
The new Sony's are a great step forward in compactness. And the lenses and image quality is amazing, as good as the big, heavy cameras. But: autofocus is slow, and the shutter is very noisy, for some reason.
But that'll get fixed. The important thing is that somebody is actually doing something to take the mirrorless revolution to full frame, and I hope this will put pressure on the pro field. For sports photographers, it will still be a CaNikon world for a while, but for many others, landscape photographers for example, minimal size and weight for maximum image quality is very important, so I have no doubt this will at least grab some market share.
David Pogue has a big article on something which (and that's a good thing) has been a hobby-horse of his for a while: getting big sensors into small cameras.
The challenge is not physics, Sony says, but cost and difficulty. Nobody puts big sensors into small cameras because the price would be too high for consumers and because it would involve redesigning everything: body, lenses, processor and so on.
(And the 5D series was even known as the "relatively compact" full-frame cameras!
This is another big blow for what they can achieve with going mirrorless.
Of course, nothing is perfect. For example, there's currently no way that Olympus's exemplary 5-axis stabilization system could be built into the Sony A7 body. It requires much more space around the sensor.
Oh, and another thing is that there are hardly any lenses yet for the durn thing. And a good lens system is not trivial, it takes years and years, if not decades to build up.
(That's one of the reasons I like Micro Four Thirds so much: over the past several years, Olympus and Panasonic have built up a delicious stable of excellent lenses, covering basically anything you may want.)