After purchasing and playing my first Magic: The Gathering (MTG) duel deck, Phyrexia vs. The Coalition, I purchased a second one - Ajani vs. Nicol Bolas. This is the first duel deck I have had that has been built around a Planeswalker type.
From my understanding of these decks, Wizards of the Coast (the developers of MTG), made these decks to be played by two people against each other. With just the basic understanding of the game, two people would be able to purchase this product, shuffle, and then start playing. You can always change the cards in the deck, or take cards out of it to add to other decks you may have, but it is not how to use the product as it was originally intended.
After playing a few games with these decks, I feel that the Ajani deck tries to swarm out a lot of creatures while gaining life at the same time. On the other hand, the Nicol deck needs time to build up a large store of mana to play some powerful cards - but meanwhile will try to counter and remove the opponents cards on the table and cards in hand. The deck lists can be found on the Wizards website. The key aspect of the game I have noticed is that whoever gets their Planeswalker out first will usually have enough of a position to win the game. A Planeswalker in the opening hand would be a huge advantage, and knowing when and when not to mulligan is critical.
For the moment, I am content to play both my duel deck sets as they are, and against their corresponding opponents. I think they are a great way for casual players or people who are just interested in playing occasionally (that do not have their own decks) an opportunity to play instantly. The only suggestion I could make would be to remove 3 cards from either deck, and include 3 more copies of each of the Planeswalker type cards.