The ability to change default settings globally
I'd give anything for the chance to globally change certain defaults (either within a template or better, for all work) -- the fill color for shapes; outline for shapes; font and size; probably others I'm not thinking of, plus my biggest frustration: "on click" for animations.
If someone has to change all these not just for each slide but within a slide multiple times, it's a HUGE frustration.
Having said all that, I am head over heels in love with PowerPoint. I abandoned it years ago (like when it first came out) and wouldn't touch it since -- until I learned it can create animations and video!! Now I'm in love with PP and forgive MS for those clunky, impossible first versions. (Well, almost.). I never cease to wonder at how quickly videos are rendered. And all the tools and variations. Ya'll do a fabulous job. Thanks.