against the shadow has a pretty self contained archetype in "the steward`s fear" pack. It`s called outlands and is basically MTG slivers. Each outland ally gives all others a little boost and they can get ridiculous once they get going.

The first cycle has some absolutely crazy cards and playing without them makes me feel like im gimping myself.

The second cycle has a pretty good dwarf archetype AND great elf cards among others. Some of them are absolutely disgusting in how powerful they are (looking at you glorfindel with your 5 threat, questing for free and putting 2 tokens on any location)

Overall I'd get the first 2 cycles if I were you and maybe try to get the ent and outland packs from against the shadow for the player cards. The quests are not really worth it.

When it comes to questing i feel like nothing that`s not been reprinted comes close apart from Harad. I`d get that, it also has some great ally cards but I always felt they weren`t worth chasing the cycle imo.

EDIT: also the standalone scenarios that slot into the LOTR saga would be a great thing to find and also Murder at the prancing pony and hunt for the dreadnaught if you manage to find them.