Strictly speaking macro photographs are 1:1 to 1:10 (10X) life size on image. These dice certainly are not this big in life, so they do meet the macro part of the challenge. Part of the problem may stem from the fact that there is really nothing in the picture to give us a sense of scale. Secondly they are immediately recognizeable as a straight rendition of dice. This cost you some points from those who were dead set on seeing something abstract in all the images.
As far as the image goes, it is a bit over exposed to me. The highlight betweent the 6 and the 4 is burned out and also a bit distracting. The background since it is not a jet black, comes across as a bit grainy. Darker here would have worked better.
Focus is very good, and depth of field was used to good advantgage.
I might have liked it a bit more had the subject not been cropped so tightly that the reflections were cut off.
DICE!!!!!!!!!
*cough cough ahem* (I'm not a dice geek.. no really.... *cough*)
I think the problem here is that this is definitely recognizable at first glance. But... it is recognizable to me. Most people won't understand what a d12 is and might see it as meeting the challenge more than I do. What I may have tried to do is get in closer to the dice so that the edges weren't as recognizable? But then you have the problem of context - it might not look like a macro, at that point, because there's nothing to compare the size of the dice to. It's sort of a tough decision but I do think that even for people who don't recognize d12s, they can see that there is a definite "subject" in your shot, making it less abstract than they might prefer.
My entry in the first Abstract Macro challenge included a d20 and got a really helpful comment from the critique club that you may be interested in looking at.
I love the colors and the reflections... Your title is great because what really makes this image so great to look at is the rainbow bits.