Although I agree with @brennon that the Lord of the Rings setting probably has a wider appeal as a gateway game than Cthulhu, my experience of beating my head against a wall trying to play the LotR LCG is that is indeed very difficult, and the deck building tends to happen between the scenarios so there is no real sense of persistence or progression; Maybe you will have a core deck that you will use over the course of a cycle, with a sideboard of cards you will drop in for each scenario, but even if you play a lot of scenarios in order it feels like playing of multiplayer video game levels that take place on single player maps, and your deck is just the loadout you pick for that map.

Arkham Horror does a much better job of weaving a narrative and even though certain scenarios are pretty darned hard, it doesn’t matter so much because if you fail, you still progress on to the next scenario, keeping your experience which you can use to upgrade your persistent deck. There will simply be a price for that failure that will in someway influence the next scenario or perhaps the conclusion to the campaign. Of course, since this is an FFG LCG you still have the same relentless release cycle but the advantage here is that unlike LotR or Netrunner, Arkham Horror is a much newer game so catching up (if you have that collectors gene) isn’t such a daunting task. Will it have the lasting appeal of the LotR game? Who can say. Certainly when you consider the game from a replayability point of view, it is like comparing a memorable single player campaign (Arkham Horror scenarios) with some great multiplayer maps (LotR scenarios). In the long run, you could end up playing LotR more but only if that is the kind of experience you are looking for.

Of course, while the story content is specific to each scenario and / or campaign, the pool of investigators and player cards is only going to get bigger so if you want to build the ‘best’ deck for your character, there will always be that drive to get at least one copy of everything. If that sounds too exhausting, @lloyd the other option is the excellent Pathfinder Adventure Card Game which is also fully cooperative.

It follows a similar release structure to the FFG games in that there is one big box release followed by a number (five, to be exact) smaller purchases on a monthly or bi-monthly cycle to ‘complete’ the story, but while you can in theory cherry pick some cards from one set to re-use them in another there really isn’t any need. Thus, Rise of the Runelords, Skull & Shackles, Wrath of the Righteous etc feel like self contained games with enough variety that you could reply them several times without feeling like you needed to invest in the next and with 30-35 scenarios in each set, it really does feel like embarking on an RPG campaign. Plus there are dice. Everybody likes rolling dice.