From the leaked screens comparing L4D2 made using Source Engine vs Source Engine 2.0, the latter looks nothing compared to Unity 5 from the demo reel at GDC which already looks meh and not as good as anything UE4 presented, let alone compared to UE4.
It seems you really don’t know what UE4 can really do : http://www.neogaf.com/forum/showpost.php?p=154489030&postcount=460