The G Flex is curved from top to bottom, unlike the Samsung Galaxy Round which has a sideways curve. It also has its buttons located on its rear, which has become a signature for LG devices. It also looks like the G Flex may have a dual-color LED flash, similar to what is found on the iPhone 5s, which should result in natural skin tone when taking pictures.
Unfortunately we aren't certain if this device will include optical image stabilization like the LG G2. In any case we wont have too long to wait as the LG G Flex is expected to be officially announced as early as next month, and may make it in time for the holiday shoppers.
source - Telefe Noticias | Federico Ini (Twitter) | The Verge