The colors. Try adding like, soft-brushing ( same color as the background) over the guy, Soft Light, and lower the opacity to about 20-60% (any of your desire). Note the "a bit more" part.
The background, and the colors are great. The render doesn't work though. Just doesn't match the coloring at all. And the edges of the stock background still show, so it doesn't fit. Other than that, it still looks pretty darn good.
I would agree that the render is just out there. It seems like you never rendered the image, you just put it in there and then blended it with layer mask/gradient to cover up most of the background, but IMO it doesn't work thus you've ended up blending the bottom left a little too much. The background is great though, nice effects, i've been trying to do a similar effect recently but with no success,lol. But yeah, maybe a change of render?
I never really render images ^^ i just use the bg smudge it put effects gradients the whole bunch over it, but i smudge the edges of the stock/render its all defaults btw, same as all my sigs, the only thing thats from the e-net is the stock
