The slope of your curves translates to how the forces are acting upon your animated objects. Understand the differences in how characters of varying mass will move. It takes more energy to initiate, stop or reverse the motion of a heavy object or character than it does to do such to a light object or character. Think of the difference in the force it requires to set a bowling ball in motion as opposed to that which is required to initiate the motion of a balloon. And similarly, the force it takes to slow, stop or reverse the motion of such objects.
Characters seem off balance.
When a biped character lifts one leg, he must shift his center of gravity over the supporting foot in order to maintain balance. Study posing and the concept of contraposto. Use yourself as a guide. Study the shifting location of your center of gravity when you transfer your weight from one foot to the other. When you walk.