I've had my 5D3 for a week now. Given the depth and breadth of the discussion surrounding this DSLR there were no major surprises. I expected to be impressed—and I have been. There have also been a few little things here and there that I didn't expect. I thought I would mention a few of them.
1. I don't get 6fps with my Sandisk Extreme III 30MB/s cards. They aren't fast enough. The Sandisk 60MB/s are.
2. The AF system is great—no, make that GREAT! However, not all lenses of a particular maximum aperture work the same. In other words, some f/4 lenses will be able to use more of the focus points than others. Put another way, some focus points may be "cross-type" with some f/4 lenses but not with others. What lenses work with particular focusing points is spelled out in the manual but there's no explanation as to why. I'd love to know. It doesn't seem related to the release date of the lens.
3. The metering system seems noticeably improved. With each new generation, Canon touts some improvement to their metering system. Honestly, I've never noticed much difference from the EOS 3 to the 10D, 5D, and 5D2. That's not the case this time.
4. Auto exposure bracketing can be up to 16 stops apart. (To be clear, that's a 16 stop difference between the darkest exposure and the brightest one. The actual DR captured can be greater than 16 stops.) I'm hard pressed to imagine a scene that couldn't be fully captured with this range of adjustment. And, unlike Nikon (as it has been explained to me at least), the interval between brackets remains fully adjustable in 1/3 stop increments.
5. LOVE the +/- five stop exposure compensation. I would love it more if one could actually see what the EC setting was when it exceeds 3 stops in either direction. You can tell if you look at the quick control display on the rear LCD; but not on the top LCD panel or, more importantly, through the viewfinder. Disappointing.
6. Many first impressions described the 5D3 as feeling more "professional" or more "robust" and "rugged" than the 5D2. I always wondered what exactly this meant. The word I would use is "heavier". The 5D3 is only 10% heavier than the 5D2 (IIRC), but I was struck by how heavy it felt. My arm is just used to picking up the 5D2, I guess. I'll get used to it.
7. Like everyone else, I read about the "silent" shooting mode. Then I listened to audio clips of the regular mode versus silent mode and I thought to myself, "It's definitely quieter but not orders-of-magnitude quieter." Then I started reading all these glowing posts about the silent mode and how amazing it was. I decided that the audio comparisons I heard must not have done it justice. Turns out that the audio clips I heard were representative. There's a difference for sure but it's not like you're going to go unnoticed if you're shooting during a worship service. You'll just be less noticed.
8. Love the "grip" on the CF door. This is emblematic of all the little things that add up to making the 5D3 a nice upgrade.
I've been (and remain) critical of Canon for their apparent lack of effort in improving the base image quality coming off the sensor—particularly in regard to dynamic range. However, I think it would be a mistake to conclude that 5D3 doesn't improve on image quality when compared to the 5D2. Better focused images improve image quality and better exposed images improve image quality. To the extent that I rely on AF for focus and AE for exposure, the quality of my images has definitely improved regardless of what has or hasn't happened with the sensor. I'm really going to enjoy using this camera body for the next three or four years.