How does power change over the course of narrative in Animal Farm?

I think that the most evident answer to this is that the
animals wrestle power away from the humans.  Mr. Jones' own inept leadership enables the
animals to rise and overwhelm him to gain control of the farm.  Power changes in this
respect, from human to animal.  However, once the pigs, in particular Napoleon, gain
control, Orwell's genius is to show that their demonstration and exercise of power is no
different than the humans.  Using the tenets and philosophies of Old Major to gain
power, the animals end up violating these ideals when the gain it.  The control of the
farm and the maintenance of their political power resides in acting as humans in animal
form.  It is in this vein that the pigs are able to broker deals and negotiations with
humans, force loyalty from the animals through violence and force, engage in alcohol
consumption, and present a vision of control that as just as strong hierarchy as when
the humans were in control.  In the end, when the animals look through the window and
see no difference between the pigs and the humans, they are right in their vision. 
Power has changed in terms of human replaced by animal, but in the end, there is little
difference in terms of the control and the structure of rule in which the animals, as a
whole, lack any substantive notion of power.