This is just a quick list of things I've felt would improve the game.

1.) Optional Match Making option to exclude Antagonists.
2.) An option to narrow down the level gap of fellow players.
3.) The addition of character and weapon skins as rewards.
4.) Better balance between characters special powers. Example being Ayana's tether which appears to have very limited purpose, versus Harec who can fly, or Doldren who can teleport. A fix in this case would be to cause the tether to drain the life of the enemy, reinforcing her own as a armor boost while tethered.
5.) High score: A more nuanced score keeping system that covers all modes and allows the player to track their achievements.
6.) Offline mode. An offline mode which allows the game to be played without an internet connection, but that has no rewards other then keeping a high score.
7.) Unlockable cards. Seems a waste that cards are gained at random. I feel like it would be interesting to actually gain cards as rewards rather a random draw.

That's all I got for now. Loving the game, hope to see it continue and expand!