What Capt. Pete said. The NAUI Master Diver class, if taught properly, is meant to kick your butt. Its syllabus incorporates various 'real-life' situations (navigation, search and recovery, deep-diving, and so on), and teaches you how to deal with them. I waited about 18-months and 70-dives before progressing from NAUI AOW to Master Diver, partly because the course's dive requirements necessitate that you build on and expand your existing knowledge, and I am so glad I had even that modest amount of experience under my belt before tacking this course. For the Navigation component of the MastDiver course, for example, I was requested to plan a [shore] dive. Sure, I learned to use a compass and so on in AOW, but that's a whole different ball-game to everything that goes into planning a shore dive in a new location properly - asking resort staff about their favorite places to see, getting the corresponding compass bearings/natural navigation aids, seeking advice on prevailing currents, and drawing a map based on their comments. My instructor trailed along as part of the group, and made it clear that this was MY shooting match. Once I thought I was finished the Navigation component, noooo...she had no problem turning to me in the middle of a 'pleasure' dive and telling me to take over and lead the way home...just to make sure my training was being utilized. Real world situations are what's emphasized, and it's invaluable. I was also expected to be the dummy for demonstrating various skills: my instructor would point to me and ask me to perform fin pivots, mask-clearing, regulator recovery, and so on for the benefit of open water divers in our group. And over, and over, and over again!
I do NOT want to get into a PADI vs NAUI vs SSI vs whatever shouting match, but I will say this: the components of the NAUI Master Diver course are exacting and challenging. I feel it gave me the foundation to be a solid diver, as well as pointers on how to continually improve. Moroever, the academic component of the course is pretty damn extensive. If a NAUI Master Diver decides to become a DM, for example, he/she should have no trouble - or surprises - when it comes to the math and physics component of the DM exam.
To the OP - I hope you do the course, and get as much out of it as I did.