If you enjoy Duels of the Planeswalkers you might also enjoy Magic: Online.
[url=]http://www.wizards.com/Magic/digital/MagicOnline.aspx[/url] You can either play as a trial account with preset decks, or pay $9.99 to set up a new account which includes over 300 cards as well as what's called "Planeswalker" cards, which cannot be traded.
It's a nifty game, though you have to buy extra cards just like in real life.
I've heard good things about Duels, might pick it up, though there's not much point since I already play the Online version.

I tried Online after Duels and meh..it's just too outdated and unintuitive...even without customization, I'd rather play Duels. Hopefully they overhaul it in the future. I heard they are planning on it.

Tried out the demo of Duels and liked it...I'm hoping it maybe pops up as a daily deal during the current sale.

Finished the main campaign and started the exp campaign, but decided to go online. I must be getting lucky because I this is my first Magic action and I am 4-0 up so far in ranked matches lol. This game is cool.

This game is Magic without any personality. Zero customization defeats what I believe to be the entire point of a CCG. Many of the decks are straight up counters to other decks in the set. Some probably don't even have the potential to beat others. Say, for example, you use the overrun deck and someone else uses the elves with forestwalk deck. The only one I've found to hold up universally is the artifact deck.
It's a lazy, oversimplified implementation of a great game. I'd rather play the old Microprose version.