Wow, the arena is amazing. I'm impressed on how it turned out. Good Job on that.
Yet it lacks something.
I would like to see additions like for example, a replay feature where one is able to watch the matches people played against them at the next log-in. That would be spectacular.
Also, the rewards for each league should be balanced better, IMO.
EDIT: One more thing, being able to spontaneously try out your t500 deck to get the right amount of pillars etc.. would be a further fabulous feature. Or, at least being able to get the usual deck-code so that we can manually try it out...