Hi!
Times ago I was receiving emails from blizzard every month with interesting stats about my gameplay like: win rates, wins in a row, etc. Also in the previous version of HS, there were stats for all wins in-game, now they are separated by class. Also, on other sites, if you link your account you can easily see the cards, that you own, which of them are golden, how much dust you can gain, etc. In-game this is user experience disaster right now. So, you can make a webpage related, connected to the user profile (Just like in Diablo and other games) with all kinds of public/private stats and an easy way for the players to keep an eye for them. Overall win-rate, win-rate by class, time spend in-game during a day, week, month, games played, games won, wins in a row, list of all in-game achievements, both claimed and not. List of cards owned/missing, golden, normal, diamond, list of cardbacks owned, missing. Arena, Duels, BG stats, stats by modes and so much more.
Best regards!