Diablo III features a vast array of enemies to bludgeon to death. They're more intelligent this time around, featuring improved AI that will force the player to adopt additional tactics besides simply rushing in for the kill. The bosses and so-called 'mini-bosses' are more personalised as well; they've been beefed up in scale and appearance so that they make much more of an impact than they did in Diablo II.
Another key change is the introduction of unique 'critical hit' death animations for enemies. If monsters die at the hands of a critical hit their deaths will be especially gory and will mirror the damage type that killed them (so, for example, sparks will fly if it was lightning damage, or flame will engulf them if it was fire damage).