i think law isn't really that hard, its just reading books...a lot of books. THere are no sort of intellectual barriers per se, which would stop anyone from actually learning the content of law, practising law I admit requires certain personal attributes etc, but contentwise (which this thread refers to) law is just reading.
In terms of difficulty i think a lot of science subjects, for example, my bro gave me his books from his first yr of space engineering and the statics and dynamics subjects are incomprehendable, both conceptually and in some cases physically haha...where as i don't think you would come accross that same sort of bizarre feeling when reading an arts book on history or a book on contract law...although its comparable to opening a book written completely in Swahili in an arts langauge course
Also maths subjects like statistics that are simply there to mess with your mind I would think are pretty difficult to conceptually wrap your head round, contentwise.
Basically, I think its the subjects that require conceptual learning, rather than wrote learning, that have the more difficult content