So, what's the problem? It's hard to explain, and you'll certainly need to check out the embedded video below, but let's just say that it seems like the optical image stabilizing gizmo is going nuts, creating extremely wavy footage. Unfortunately, the issue isn't limited to just video capture, with owners reporting that the camera is basically altogether useless.
On the bright side, Apple is likely already well-aware of the issue and several iPhone 6 Plus owners report having had their camera module or entire devices replaced thanks to its warranty. Unfortunately, if you're currently away from the device's home country, you'll likely either have to ship it back home or pay up at a local brick & mortar.
Tough start for Apple's first phablet.