In the latest developer diary, it's been revealed that weapon speeds will now be standardized by weapon level and type, making sure that all one-hand maces of the same level swing at the same speed. This is key, as previously players were taking slower weapons to maximize their damage, even if it wasn't appropriate for their class. (Turbine was looking at you, mace wielding burglars.) Weapons have also gotten increased speed but lowered damage to compensate for their fast swing rate.
Animations were another sticking point, and Turbine has created a new skill type that will immediately start upon being pushed, without the player waiting for the animation to complete. The other new skill type, fast skills, will immediately start after the last animation completes, ignoring the standard wait time after the last skill. Overall, this should produce quicker, snappier combat in Siege of Mirkwood.
For all of the nitty gritty with these large changes, check out the full developer diary on the subject.