There is nothing that is intrinsically difficult but the quantity of information which has to be absorbed. Much of it, especially Air Law, is rote learning.
Are you thinking of CPL exams or ATPL? I believe the ATPL syllabus is broader than CPL.
Air Law - even more boring with knowledge of ICAO structure etc.
Human Factors - much the same only to more depth.
Comms - Again, pretty much the same but with some technical knowledge on radio wave propogation.
Met - much more in depth and covering global aspects.
Nav - I found this to be quite a step up from PPL.
Etc etc.
There's no need to be concerned; if you are thinking of the professional exams, you have to enrol with a ground school and they will help you through it.
Cheers
Whirls