One thing that might be different are nonlinear class progressions.
In 3e barbs get rage every X level, fighters get feats every X levels, etc etc.
Problem with that is that rage 1/day is awesome, rage 2/day is good, rage 5/day is often wasted. Since monsters won't have just have class levels like before they don't need the convenience of linear classes as much. Players will just look at their charts once in a blue moon when leveling characters, and dms will have their monsters just ready to go.
In 3e barbs get rage every X level, fighters get feats every X levels, etc etc.
Problem with that is that rage 1/day is awesome, rage 2/day is good, rage 5/day is often wasted. Since monsters won't have just have class levels like before they don't need the convenience of linear classes as much. Players will just look at their charts once in a blue moon when leveling characters, and dms will have their monsters just ready to go.