I really like the UI. It's sleek and functional. One idea I thought might enhance the concept is to color-code the enemy target's UI based on their level. For example, if the enemy is a higher level than you, their UI bar would be colored yellow, orange, red, or purple. If they were equivalent or lower, it would be white, blue, green, or gray. All of these are based on the level difference between the player's hero and the enemy highlighted. Allies' UI bars could be a different color to avoid confusion.
Keep up the good work!