Wait, God of War: Ascension is having an open multiplayer beta? Holy smokes, no one told me until now. But it's for real, it's open to all PlayStation Network users (Plus and otherwise) in North and South America, and will last through tomorrow (3 a.m. Tuesday EST, as the beta closes midnight PST.)
Go get your code at this site, redeem the code through the PlayStation Store, and you're downloading the beta. The site at the link also has strategy guides to acclimate you to what multiplayer has to offer.
God of War Multiplayer Beta Open: Get Your Code Here [God of War]