One thing for sure is that the art looks really great. The cards represents all the creatures you can find in Might & Magic Heroes VI and there are plenty of heroes that you can choose from. All factions from Heroes VI are available, although the Sanctuary faction just got into the card game.
Gameplay of Duel of Champions derives from its Turn Based Strategy counterpart where players must decide unit positioning and control the battlefield as best as you can. Heroes powers up at the beginning of each turn, usually giving the player one of three choices: Might, Magic or Destiny. Each of these stats will be required to summon certain cards which means choosing power ups is also a part of the overall strategy. As a rule of thumb, Might is usually required for creatures, Magic for spells and Destiny for Fortunes.
Aside from power ups, the player's hero card usually have one or two other abilities. The default ability you'll get is to pay one resource to draw a card. Do note that if you use the ability you can't power up your hero. But when your hero's Might, Magic or Destiny level already reached a certain number it would be wiser to just pay one resource to draw a card.
Duel of Champions offers two kinds of matches: Campaign and PvP. In Campaign you'll go through a set of missions which will gradually become more challenging. You can only obtain rewards once from each mission, so replaying missions will not give you anything, however through PvP you can keep leveling up. Do remember that as with most TCGs, those with better cards would most likely win. But that doesn't mean that you can't win with a weaker deck. There are achievements to get which will reward you with various packs or cards which will in turn strengthen your deck.
What worries me about Duel of Champions is its longetivity. Most TCG have various cards and expand it's card list every few month through expansion packs. Duel of Champions might be able to to this but the game is limited by the amount of creatures available in Heroes VI and as such shouldn't be having too many new cards aside from neutral creatures. It would be nice if they add more creatures that's not available in heroes VI but I really doubt that.
Overall, Duel of Champions is a good Online TCG choice for those who likes the Might and Magic series or Trading Card Games in general. The game doesn't waste too much time and the gameplay is quite easy to learn and pretty straightforward. I had fun with it, and you might too.