The biggest change is that you can no longer power attack friendly models - meaning it is now much more difficult to knock down enemy models by using your own models to line up the slam. This is a huge benefit for high-DEF warcasters such as Ashlynn and Constance Blaize, and should (theoretically) let them take better advantage of their rather absurdly potent melee abilities without the constant knock-down assassination run fear.
The next biggest change for my lists is the Rhulic Hammer Strike Theme - it's awesome! An additional +2" deployment zone, free Artillery Corps or Bokurs, and 3" reposition on all Heavy 'Jacks and Artillery Corps. Artillery Corps and Heavies form the core of my Ossrum lists already, so the benefits line up really well.
But enough talk - on to the lists!