Every area of the law is interesting in its own way. American civil procedure is unique for his rules of discovery, adversarial nature, and federalism (state and federal law).
Even though the actual Federal Rule of Civil Procedure are fairly short, the application of the laws to a set of facts can easily be complicated. For example - what should be the citizenship of a corporation, for jurisdiction purposes, HQ or place of registration? Actually, Supreme Court has recently decided in 2010, 2011? that it is the HQ or nerve center, but these debates have been going on for some time now.
It's interesting to see how little has changed in the law from the 1970s to now, at least in certain areas of the law like civil procedure and contracts.