Is there a difficulty rating for the 3 first scenarios

I recall lord of the ring lcg had scenarios rating

Is this considered more casual than the LCG? It takes much more time to finish a session

My personal rating for the first three scenarios (for what it's worth):

Mind you, I always play solo.

Margath

Easiest of the three, but not per definition a walk in the park.

Vorakesh

Most difficult one of the three. Solo undoable without any house rules regarding the number of zombies spawning. (I use the following rule for spawning zombies: X+1, where X is the number of players).

Ariad

Pretty difficult solo, but always tantalizingly close to victory, therefore a much better experience than the Vorakesh-scenario. Played it 3 times until now, and I just know that someday I will succeed.

Hope this helps a bit.

I'll say that windforce's assessment is accurate from a solo player's standpoint but if you intend to play with a party I would definitely say that Vorakesh is the easiest for the reasons stated. With more players it's much easier to keep the zombie issue on lock. Ariad I'm actually getting in the mail this week so I let you know when I find out.