WCF is wholly unsuitable for the front-end networking of multiplayer games. It can work fine for back-end service-to-service communications.
Lidgren is a C# game networking library. I don't know how easy it would be to integrate with Unity, whether the assemblies would work as-is, and such, but it might be worth a shot.
It works good with unity. But I have to poll for new messages instead of catching it in a observer pattern. I currently got this polling working but I actually want to extend it with a observer pattern so I can override something like void OnGameWorldChanged(). But first I want to familiarize myself a bit more and have some sort of chat/lobby application with rooms.