The single player is fine, but the multiplayer aspect is the reason why I bought this. Battles against the AI feels a bit empty. It's nice to win against another player, and more fulfilling to lose as well.
You only choose from preconstructed decks though, unlike the MTGO game. This is probably because their design was to"balance" the decks (as well as to be newbie or casual friendly).
As a semi-competitive "Magic Online" player, I found this version of the game to be an ok distraction and certainly worth the $10. It's like "arcade" Magic. It's not very deep, but fun to play in short bursts.
The ai is stupid and won't be any fun after you play through the campaign once. Multiplayer is a nice diversion if you just want to shuffle up a random deck and play but doesn't give you much control over what cards you play with. --- http://img704.imageshack.us/img704/297/keyboardwut.jpg
Single player is the best for unlocking cards and learning how a deck plays, though if you don't mind doing that against a player then you can do that too --- Currently Playing: Modern Warfare 2, Mass Effect 2, Magic: The Gathering - Duels of the Planeswalkers