I'll just list all the features that I think SE needs.
Merchant - Card page navigation/Card Search/Sort by:..(Hero, Ability, Ally, etc)(this should be prioritized the most if not my other suggestions)
Friend/Guild system
World/Guild/Private chat
In-battle sound effects.
Match history
Daily login rewards/event
In-battle emoticons something like laugh, smilies, taunts(since i noticed no one talks much in QM)
Would make the game much better imo. Though I don't expect my suggestions to be implemented instantly.