Boring. I know Monday puzzles are supposed to be on the easy side, but this one just didn't have much zip. I got OPERATING SYSTEM (37A: Windows or Unix) without any crosses. In fact, there were very few that I needed crosses for. GEENA (32A: Oscar winner Davis) and GILDA (32D: Funny Radner) seem a little old-fashioned. As does LIEIN (50D: Pacifists' protest demonstration). Being from Boston, I don't particularly like seeing AROD in the grid, nor do I care for the religious slant of ORIGINALSIN. The somewhat hip answer FRONTS (10D: Is the lead singer of) actually feels a little out of place.
I know that I am not this puzzle's intended audience, but I have enjoyed easy puzzles before. Not this one.
p.s. The aforementioned "Operating System" is an example showing the "system" of the theme, which is two-word phrases where the words start with S and O.