Extremely excellent to a point..
The multiplayer is a also extremely fun and if your playing with friends on the higher difficulties then it becomes an extremely addictive tactical killing frenzy (whether its you or the enemy being killed changes quite often though lol.) in addition to the integration with the single player. This integration is unique and if it has been done before I have never seen it, its a very interesting concept but it seems a little to cut and dry to me. When I first heard about the theater at war I was kind of hoping to had a little bit of strategy to the overall mix to help affect the ending but in all reality it simply multiplies a different score. Still good and alot of fun.
In addition, buying the booster decks and packs (though it does seem odd and reminiscent of Magic the Gathering or other tcgs at first) is part of what adds to the addiction of multiplayer. It forces you to make do with what you have and adds just a little more tactical gameplay overall.