I have owned this game for over three years now and am currently making a concerted effort to work my way through some of the expansion boxes. There is so much content available that i doubt i will ever own it all, however i do really enjoy the adventure questing it provides. Whilst expanding your player cards is important, and deck building will improve your chances of success, i generally get more excitement from finding new quests i enjoy. As i play solo with one deck, some quest rules do occasionally become overly difficult, but rather than ditch a quest i like i may try to adapt the rules to better suit the solo experience.
So far i have found Khazad Dum and Dwarrowdelf cycle the best overall set for quests, this is for their reasonable difficulty levels and the general theme, fun and engagement i felt while playing. The Mirkwood Cycle is important to build up player cards, but these quests are more mixed in terms of enjoyment, however they are usually easier to play against than later cycles. I skipped the outlands theme of the Numenor box and cycle, preferring to fight monsters than human enemies, and generally these quests are considered very tough. That said, I found Isengaard and Ringmaker Cycle extremely hard and sometimes frustrating anyway, with their time mechanic especially tough to enjoy. The Lost Realm box quests has been much more enjoyable, although the box is still quite a tough experience it seems fairer.
The saga boxes are a mixed bunch and i am cherry picking these at the moment, the Hobbit boxes are largely miss-able unless you want to build a better Dwarf deck, as a number of these quests are frustrating to play through. The Black Riders is a very good saga box both for building a hobbit deck, and also has nice quests that are not overly hard to beat with a solo deck. My more recent addition of Flame of the West is also another strong saga expansions to consider.
My preferred deluxe box sets for quests considering both the box itself and the cycle they support are :
1. Khazad Dum & Dwarrowdelf – great quests with excellent undergound tunnels theme, mostly a moderate difficulty level that can be played solo.
2. Sands of Harad & Haradrim – a desert theme with amazing artwork and I have high hopes for this series.
3. Lost Realm & Angmar – involving storyline quests, nice side quests addition, tough but just about playable solo (until the last two scenarios of the cycle).
4. Flame of the West – great artwork, strong heroes and some nice varied quests featuring the undead, corsairs and an epic battle to defend a city.
5. Mirkwood – varied quest cycle, generally easier than all later cycles and important to build up player cards, probably the best place for newcomers to start.
6. Black Riders – moderate difficulty, essential for hobbits cards and quests, an alternative collectors path going into the saga series rather than cycles.
7. Grey Havens & Dreamchaser – not purchased yet, ship scenarios look unique but fiddly to play, the middle of the cycle has great looking quests though.
8. Heirs of Numenor & Shadow – not purchased yet, an outlands theme and more battle orientated, the initial box quests are considered very hard.
9. Voice of Isengard & Ringmaker – overly hard to solo and a time mechanic is often frustrating, but the cycle does have a couple of redeeming quests.
10. Hobbits – varied quests over two boxes but quest design is often fiddly, complicated and even annoying, the second box quests are better than the first.
Other Sagas – i have not yet purchased Road Darkens, Treason of Saruman and Land of Shadow so am unable to comment on these, the quest storylines here are similar to those in some of the cycles.
More details on my favoured quests are found here > Lord of the Rings LCG