First and most importantly, the core rolling mechanism is that instead of trying to roll over a difficulty level to succeed, we now have a roll (plus ability bonus) instead equal to a difficulty in order to succeed. This means that defense is now what your attack roll + ability bonus has to be in order to successfully attack that target (equal to or greater than the target's defense.)
Second, we are now again listing character's defense explicitly (after tgh/2.)
Third, all healing rolls now have a difficulty level of 10 (they used to vary more than this.)