Yes it is being used, link to short games list below
it depends, the major draw card for me for UE4 is the blueprints system and how simple it is to make something that just works, even in a multiplayer environment.
Is the documentation outdated? Yes
Do they rename functions? Yes
Can it be annoying? Yes
But in terms of out of the box usability, i (personally) find UE4 simpler than Unity.