This one's a beauty - my first MAC polish is a glittery duochrome which shifts from bronze to purple and gold with tiny flecks of blue. By itself this polish is pretty hideous - a slightly sparkly swamp green polish and the color shift does not show up like it does in the bottle. Instead, to achieve the full effect, I have opted to layer it over black.
*faints* It's so pretty! i'm surprised at how nice the formula was (layered, of course) and the brush was pretty good. I liked the rubber cap, as well. Overall, I probably wouldn't pay this much for a normal polish from MAC, but this is worth it just for the color shift.
Do you own any MAC polishes?