I regretted buying the Hobbit rulebook, so my review is a little skewed.
The book adds a bunch of new rules to the system. Weapons now have special stikes. Depending on what you are armed with you could knock an enemy prone, stun them, or increase your strength when attacking your foe. Monsters get a series of brutal power attacks, giving them extra options in combat as well. In the character section a number of the special characters also have a ability called 'Burly' which lets them ignore the penalty for using a two-handed weapon.
I enjoy the base LotR rules, and wish I had stuck with that, rather than pay $90 for the Hobbit rulebook. For that money I would have expected it to contain the stats for characters in all three movies, not just the first one.