I've been working on a multiplayer card/board game with some friends! We've been using Unity (C#) and its services like Relay and Lobby. Working with Unity has been pretty solid so far but I cannot recommend Relay and Lobby (now multiplayer tools) as their docs are missing a lot of crucial details such as how to preform host migrations.
We are hoping people who enjoy Magic/Hearthstone will appreciate the complexity and mind-bending nature of this game: