I can't really critique much, maybe a lack of warmer colors near the core, overdodging a bit in the center. I concede it feels like looking at a frame capture from something like the Fountain, so it feels more like concept art than something I would expect to stand on its own. Just my two cents.
This is really cool! I love the layers upon layers. I love the expression and the pose of the man. I love that you can see his muscles/tendions in the hands.....well really I love it all lol. Great job.