Well recognized.
The first as well as the second german ... empires/'Reiche' were much more of a federal or confederational make-up, than every other 'Empire' of history (I know of).
The other empires were more of a straight downwards 'rule' or 'authoritarian', if you like.
"Empire" comes from the latin word "imperium" which comes from the verb for 'command'. Hence in an empire the emperor 'commands' through the downward chain of his subordinates.
In the german versions, the 'emperor' was at first constrained by juridical laws, which clearly defined, what he was able to do and order and ... what not.
Because :
for becomming ... and staying emperor he was dependant on a whole bunch of other nobles, dukes, etc., who all were very keen to keep their own power.
IMHO the most important difference to other empires was the juridical side. Even the emperor was bound to law, made not by him, with detailed insrtructions how such laws were to be made, whereas in 'ordinary' empies the emperor was also the source of law by himself, he 'set' or 'made' law.
Irony of history : the "Third Reich" was from its internal politics and functioning much more like the 'ordinary' empires, than the first and secong derman empires or ... "Reiche".