The game is pretty laid back until level 20 when you reach Ettenmoors and then Angmar. Ive seen crazy shit in those zones during closed beta. Though i never made it further than level 22.
The chapter quests - 1 through 9 is pretty easy stuff.. that range can be done within like 2 hours of hard work, no problem. There are 4 dungeon areas within that span I think.
Chapter 10 involves killing a mob in the Barrow Downs, a big witch type of mob, shes kinda hard unless your group is fairly good at using their brain. Shes easy if you have a burglar stun her while you take out the birds though, just remember that.
Chapter 11 is where the game finally gets hard. We had a group of level 13-15's, and it was no joke. Wiped twice.. and the final boss down there is a BITCH, haha. He full heals himself halfway through, at around the time your entire group is fucked on health. It was intense when we barely beat him.
Chapter 11 is what gave me hope for the rest of the game and I know its going to be awesome in the later levels.
Levels 1-15 will be slow, no doubt. Just questing and killing wolves and shit like Niall said. Stephen Colbert would be proud at all the Bear quests