Canon finally released their mythical 'consumer' full-frame camera, the 6D, right on the heels of Nikon doing the same. Both look like very nice cameras which I'm sure will take delightful pictures, their sensors being of the same pedigree as the ones in the pro gear and all. As the price comes down the features that differentiate become more specialized and tend towards things like user interface and handling and the like. I haven't played with the new 6D yet, but based on spec sheets and reading a handful of hands-ons, I've got some thoughts, especially on how it compares to the 5D Mark III which I use.
As far as overall image quality goes, I'd expect the new camera to be very similar to the latest 5D. A few less pixels that nobody is going to miss. It's got the same screen, way crappier AF, is a little lighter & smaller and costs $1400 less. That's $1400 that could buy some nice glass. And I'd rather have this body and an L prime than the 5D3 and some crappy zoom. That said, I personally don't mind a little heft in my camera and the 5D fits my hand perfectly.
A few people have written me saying that the 5D3 should have had the GPS and WiFi capabilities that are in the new 6D. Maybe. I wouldn't have turned them away if they had, but computers are always getting better and cheaper (I would have loved an original iPhone with 4G too), plus for the kind of stuff I shoot, neither of those capabilities are necessary. GPS would be nice for landscape photographers I'm sure, but I only do that kind of work once a year on vacation. And to be honest, I sort of like having a memory of where a picture was taken in the internal map in my head. Clicking a link and having it open Google Maps takes some of the fun out of it for me.
WiFi on the other hand would be great while shooting wireless tethered in a studio situation. Assuming of course that it works that way. In the spec sheets that I've seen it's designed to send pictures from camera to camera, or to a printer, or to a smartphone, or to use an app to control the camera from a smartphone. All of that makes me shrug. However if you could have it connect to and write the images to a shared folder on your network, well that would start being interesting, but it doesn't seem like that's what the engineers had in mind. I could be wrong.
Overall it looks pretty nice. Some people are saying that the new Nikon D600 is the same price with better features and that might be true. I guess if you were starting nothing you could choose one or the other, but I doubt the differences are going to make someone with an investment in one brand's glass switch teams. Finally though, it's just another tool. Nothing earth-shattering and nothing that's going to make you take better pictures. That's YOUR job.