If you ask me I find Duels to be a total failure.
Early Access was complete nonsense.
Blizzard was like: “Hey guys, here is this new Mode. We want your feed back. However you need to give us at least 40$ to try it”. Now that the duels is out for everyone. it feels like a pile of garbage.
I have played few games and I can say that if you haven’t invested in building a card collections you will have terrible time with this mode. it is nearly impossible to win a game vs a higher spender users.
I guess you could argue that because you can only add 1 of each card and the starting deck is only 16 cards. it would not cost you that much money or dust to make decent starting builds. But the difference of having that one legendary card that can win you a game in a deck of 30 and in a deck of 16 is a huge difference in this mode.
Duels is worse then the normal/ranked mode.
You need to build a deck with fewer cards of higher rarity. (higher average cost per card)
Random hero. You can not build one or two decks ( Because if you have one or two decent decks you will be at disadvantage when those classes are not offered *Note this is irrelevant if you play in normal duels mode as you can retire without loosing anything )
hero powers locked behind 10 x epic cards ( you have 4-5% for epic card from a pack)
treasures locked behind 100 x unique expansion cards. (this would probably take you 25-35 packs) another one locked behind 20x epic cards from the previous expansion. (Now that is some huge money grab you need to buy packs from expansion that will be rotated out before the one you are currently playing in)
Even if you spend a lot of money and have all the cards. You still get to be frustrated by the heavy RNG system. Spending money/dust will give you advantage to probably round 3-4 and that is until all the new players realize they are not welcome in this game mode.
Seeing Battlegrounds I personally had high hopes for duels as my favorite game mode is in the solo adventures Tombs of Terror. which kind of resembles duels here and there. I have beaten the heroic mode with every single class and i am currently working on beating it with every single hero power and next with every single starting treasure.
At the end of the day I find Duels to be a big disappointment. For me It is yet another game mode that tries to milk users for money.