Of the classes, I think by far the most important one was buoyancy... we did it third (our second day there) and it really, really helped with the rest of our weeks worth of diving... it wasn't just the techniques, it was the feedback from the instructor on how to improve that helped. I saw a video of me diving later in the week, everything was streamlined and trim, I was horizontal, using breath control to move up, around and through the coral beds without touching anything and with my hands tucked properly and I was like "Whoa! That is me?".
This is wonderful, and that's what an AOW buoyancy class should do!