Still enjoying myself - just unlocked the second arena/level/dungeon (I forget the exact term and don't have my device in front of me), but I've been staying in the first to get better with easier enemies.
Two things: the option to add the attack-aura to the entire screen and not just above the enemy is (quite literally in the game) a lifesaver. A little feature that went a long way, thank you!
And the second - would you consider adding an endless/zen level? Some kind of "training ground" type of thing? I enjoy the fast pace of the battles themselves, but I'd also love the option to just dive in without any enemies or time limits.