I have played a variation on this deck since I started about a year ago and after much thought and editing it will be hard pressed to improve it, but I'm open to suggestions. This deck is well balanced and can take on just about any encounter, especially if it's will power you need! It's greatest weakness is any quest that punishes you for losing allies, because chump blocking is the primary way to defend. O Lórien! is the card to mulligan for, as it will let you bring out allies much easier. You almost don't need Song of Kings, but it's nice to have if you are short on leadership resources. I used to run this with Steward, but you truly don't need it with O Lórien! in there. Then Galadriel can pine for Nenya and Light of Valinor if need be.
Your threat should raise like normal until, Light of Valinor is found and if you need more threat reduction I would recommend adding Island Amid Perils, and The Galadhrim's Greeting. Unexpected Courage is a must on Galadriel after Nenya is found.
The best defender in this deck is the Defender of the Naith, and, between Arwen Undómiel, The Tree People, and Feigned Voices, can be boosted up to four defense for multiple turns if need be. If you need a bit more defense, add Desperate Defense to make him a six, plus it will ready him if no damage was taken. Also, Feigned Voices is awesome and can be reshuffled back into your deck with the Galadhrim Weaver.
As for attacking, Glorfindel can wreck things with Fair and Perilous, especially if you can boost his will power with Elrond's Counsel and Celebrían's Stone. For further willpower/attack power, add in The Favor of the Lady and the Star Brooch. Between Glorfindel's and your allies attack, your enemies will be annihilated.
The only inconsistency with this deck is the consistency on defense, however, in a co-op game life is much easier if someone has Beregond, Beregond or another epic sentinel defender, and your day will be glorious!