Canon doubled the number of megapixels for their EOS DSLR in one fell swoop with the 5DS. While high megapixel count doesn't always translate into better images, with the full frame sensor, the 5DS has a significantly higher resolution than other cameras in the category. The 50 megapixel sensor is capable of capturing images with a 8688 x 5792 resolution--by comparison, the 22 megapixel full frame Canon EOS 5D Mark III has a resolution of 5760x3840. That high resolution will be quite enticing for photographers who can't decided between full frame and medium format--or who can't afford medium format.
While the high resolution is obviously the camera's biggest selling point, we expect the 5DS to excel as a camera overall. It sports a 61-point autofocus system that should perform quite well. The burst speed of 5 fps is just average for the category, but with such a high resolution, we didn't expect high speeds. We would have liked to see a higher ISO limit than 12800, but that's certainly no deal breaker. All the elements you'd expect from a high-end DSLR--like a secondary screen at the top of the camera and dual SD card slots are also built in to the 5DS.
While Canon is known for having solid video quality, the 5DS is a little behind here. The maximum frame rate is just 30 fps and not the higher 60 fps. And with such a high resolution, users can only record at full size for about 11 minutes with an 8 GB memory card.
Consumers should always be aware though that megapixels doesn't directly translate into better images. The camera has excellent resolution, but comparing DXO Mark sensor scores to similar models, the D5S suffers from more noise at high ISOs and a smaller synamic range than even cameras priced much lower.
Canon released the 5DS R at the same time--it's the same camera, except eliminates the optical low pass filter. The elimination of that filter helps enhance detail, though puts some images more at risk for moire.