In short, the alleged gameplay trailer shows a man with a shoulder-mounted light device surveying a dim room, then firing on and fleeing from a yellow-eyed, many-armed creature. The monster taunts him from behind the door, "almost singing" the words "I have found you" before the game's title appears on the screen and the trailer ends. OsirisBlack says most of what they were shown was live gameplay rather than a cutscene, and specifically called at the lighting and physics as being "on another level".
There's no way to prove that this is actually a thing and not just OsirisBlack describing a dream they had the other night, or something. Their previous history with leaks helps lend this one some credence, but it's still worth taking with several grains of salt. Honestly, the most interesting part to me is that Ready At Dawn may still be trying to make The Order franchise work after the first one was so poorly received - I'm always on board for a redemption arc, especially when it involves steampunk Knights of the Round Table fighting monsters.