Compared to the 5D Mark II, the Mark III looks more curvaceous and organic. The cleaner hood and wider lens mount gives it a strong stance, but it also looks more refined, with matte buttons, subtler cut lines for the buttons and more definition in the back hand rest. The camera feels comfortable in the hands, with a good grip and heft.
Acoustically sensitive photographers may like to know that special attention was paid to the Mark III's shutter sound, which is distinctive from the Mark II's and quite pleasing (for those interested to know how it sounds like, check out the video on the first page). There's an optional silent shooting mode which will mute the shutter sound somewhat but it also reduces the maximum shooting speed to three frames per second. This feature made quite a difference when we were shooting a concert as we found out firsthand when switching camera bodies from Mark II to the Mark III; it was noticeably less obtrusive in that quiet environment.
Photographers used to their 5D Mark IIs and are thinking to upgrade to the newcomer will however have to contend with some re-learning as the controls and usage differs some. The On/Off switch has been shifted to just below the top Mode dial while the Menu and Info buttons have also been moved upwards (refer to the photo below and above for more clarity). The Mode dial itself comes with a lock to prevent accidental changes since the on/off control is now in very close proximity. Further to that, there are no separate magnify in and out buttons on the Mark III. So to zoom in on an image now requires pressing the magnify button and then using the main dial to zoom in and out (it takes a while getting used to).
The Mark III gains a new 'Q' button which provides you immediate access to the Quick Control screen where you can view and change essential settings like AF mode, white balance and ISO speeds (this was previously accessed via pressing down on the multi-controller/joystick on the Mark II).
The Mark III also has a Live View/movie mode switch, like the one on the EOS 7D. The switch indicates the camera's shooting mode, either stills or video, pressing the center Start/Stop button activates Live View while in stills mode, and pressing it in video mode starts and stops movie recording. Besides the switch, the Mark III also has a 7D-like lock switch, when engaged it will lock the main dial, control dial and multi-controller from moving. The top plate's controls are left unchanged, except for the additional of an M-Fn (multi-function) button which is responsible for changing AF area selection mode.