Great, but one problem that I have, and probably evryone else will too is that you have to know wo is playing. Duels are OK like this because you organise it yourself, but this, I think should have a lobby, with a list of all the matches currently being played. But like I said, great stuff.
Now more of a request than feedback. How about a 'game log', that records what cards are played, which slots creatures go into, which creatures/permanents are targeted, who by, and possibly even a feature that, if you put the log into it, would play the game agian, as if you were spectating. If the last bit was put in, I suppose the raw output would be as some sort of code that is readable by the game, then can be either translated into english, or replayed. Or both, obviously.