Looking really nice, there. A couple things, though:
That’s one fearsome outie of a belly-button. XD
Another thing is you didn’t leave space between his chest muscles and his abs. There’s another ridge of muscle between there, that and the ribcage. The abs don’t start right up there.
Also, his shoulder seems to bend too much. The chest muscle should wrap across to the shoulder, not bend like that at the armpit.
Edit: Holy crap, that was a typo and a half, in the last sentence I typed ‘should’ where I meant to type ‘shoulder’
Edit: Twice in the same sentence. I’m a freakin’ genius.