The muscle anatomy isn't bad, but his arms are waaaay too short. I would work on the positioning of the ribcage/torso and the overall shape and size of the cranium. This is defiantly an ambitious project. I would focus on getting solid proportions before blazing into the clothing.
His skull/neck area looks a bit thick from the side. It's a great start, like JadeEyePanda said, it would be good to have an idea of what you're going for. Whether you will need gloves, or fix up the hand anatomy a bit, same with the feet and stomach regions.