I have finished Andrew Riggsby's book on Roman law and can highly recommend it for an undergraduate course in Roman law or as a supplement for a JD-level class in legal history. In terms that are exceptionally clear (perhaps too clear at times), Riggsby lays out the basic concepts of Roman law over the course of the Republic and Empire. More than many other texts, he tries to explain how much (or little) Roman law had to do with everyday life in Rome's territories outside the city itself. His handling of the sources and adjudication of religious law was very helpful.
On the one hand, Riggsby is careful not to overplay the certainty of his conclusions when documentary evidence is lacking. On the other hand, he may be faulted for oversimplifying his subject at times. That oversimplification, however, does much to make the subject comprehensible to the non-specialist (which is most of us).