I agree, the tone is appealing and the shading is very well done. I even like the little "god ray" coming through his hand even though I think it is a little brighter than the background behind it. I think what really sells that tone is how the black lines are slightly less saturated on Hulk compared to the foreground. It gives him a nice depth in the atmosphere.
I really like the tone you used and your shading is great! It caught my eye instantly - nice work!
If I had to pick one thing for feedback I would have to say that the rocks in the foreground are a little distracting because they are so white compaired to the rest of the image. My eyes get pulled down there when I really want to be looking at the hulk. Maybe just tone them down a bit.