Acrylic is great stuff. I'll admit that I had a bias against the medium since all the serious painters use oil, but I really liked manipulating its transparencies for atmospheric effects. I think they key is to buy a lot of intermediate pigments to minimize mixing and muddiness. I also tried masking (courtesy of Youtube) to get a prismatic thing going on - not quite resolved yet but I do like the results so far.
Our models were Brian and Jen, both young, goodlooking, and total professionals. It was a pleasure to work with them.