Kojima Productions is currently livestreaming the entire Metal Gear Solid 5: The Phantom Pain E3 theatre demo, first shown at E3 2014 last week, which you can watch above.
The Phantom Pain was first announced during the Spike VGAs in 2012. We checked out the title in a hands-off demo at E3 2014 last week where we also spoke to Kojima about the "biggest game he's ever made." To learn more about Metal Gear Solid 5: Ground Zeroes, the prologue to Phantom Pain, be sure to read Polygon's review.
Update: Gameplay livestreaming has now ended. We'll update the above video with the 30-minute gameplay footage from the recent session in its entirety once it becomes available.
Update 2: The above video has been updated with footage captured from the livestream.