I have been Producing a very large game project with Unity. We have a large team, at times 50+. Our graphics aren't as state of the art as they could be but the performance of the Unity engine does not seem bad. The cross platform compatibillity is very strong. The third party tools are very strong. It's worked out well.

Unity seems like it was built with ease of of entry as a first consideration. As people do larger and more ambitious projects with it they are hitting some of the tradeoffs and limitations. I am sure UE4 is a good choice as well.