Im interested in knowing this as well.. i havent ownloaded yet because i dont want to break the game but this is a good question. +1

TLD won't "break" your game, just btw.

TLD's difficulty can't be compared to Native's, because the game mechanics are very different.
Overall, the difficulty depends on the faction you choose. Lothlorien, for example, is considered an easy faction, so it might be a good start for beginners.

I would rate it ultra easy, compared to ASOIAF, which I would rate as "for hardcore masochist people, whom love nothing more then pain, suffering, stress and making no progress in games" ;P.

Well, the mod IS actually pretty easy. I mean, my dwarf with his poleaxe fells every enemy, except trolls, with one hit (now with level 37 anyway). With only basic tactics, one can control a battlefield pretty well, and a mix of heavy cavalery from Gondor and a mix of Lothlorien/Imladris Archers make it ridiculously easy to destroy even armies that are double or triple as big in numbers. Generally the "good" forces are somewhat overpowered, having also several more tiers.

What - off topic - I don't like, although it makes sense, with a pure dwarves party, you cannot catch up to enemies, nor can you run away from them, meaning, if you have more than just a few people to hide away, you will get into every fight, including unwinnable ones, and lose all your troops.

Still, I like TLD a lot, even though I still haven't found out how to find certain "hidden" areas, or my quest "ring hunters" is just broken, because I used lvl 20 before the war breaks out, and managed to annihilate the 70+ enemy party, before I hit level 20, but got no quest progress. And their hideout near Mirkwood doesnt spawn either. So yeah, maybe more a bug.

Depends on which faction you play. Most of the challenge to me comes from the grind. Feels like you have to kill 50,000 enemies and deliver 50,000 letters for lords to get any meaningful rewards.

Now here's the cool thing: you can adjust the difficulty to your liking. For example:
Overall campaign difficulty
Rank and influence gain
War start level

You can even adjust how factions gain or lose strength, though this is to be used with caution.

Choice of side or faction also greatly affects battle and campaign difficulty.