My group always plays 4 player LotR. Osgiliath was tough. We built 4 dedicate decks, mono sphere (except for Aragorn's Leadership deck splashing some Spirit to help deal with Shadow and When Revealed effects, and tackling Threat). It took awhile before we understood how the treachery deck needs to be dealt with.
The best way to survive first turn is to load your deck with 1 or 2 cost characters. Each player Optionally engages one of the Warg units, sacrifice the cheap guy to the Warg (Warg goes back into the deck to be dealt with later), The Spirit player generally has the lowest Starting threat and must deal with the Snaga scouts, since you can build Tactics with heavy range support /sentinel pegging them off is not hard (plus there is an Event that can take them all out in one play if needed).
The deck is very tough, but doable, it really relies on having a good opening hand. The first turn Threat hit is always nasty but you can recover. Deck cycling is important.
With all of the Lore/Spirit cards that hurl progress tokens onto locations in the staging area, and with a Lore card that reduces the number of cards revealed from the Treachery deck by one things are manageable, you just need an extremely tuned deck.
Tactics/Eagles works very well in it when you get a Horn of Gondor first turn, so many characters bite the dust you can gain alot of Resources off of it, plus most of the Eagles really want to enter then leave play for good effect at moping up the Staging Area.
Team play is just so important against this deck, but beating it shouldn't be impossible if you time things right and have good deck construction skills.
We plan to play this monster Quest again with the cards from the Dwarrowdelf Cycle and Moria as they weren't out when we last played it.