You’ve lost a lot of the bulk from the concept art, which is one of the interesting parts. Also I like that the concept has the shoulder higher as if it’s uncomfortable or awkward and hunched up. The jacket and collar in the concept look more interesting as well. To be honest, the more i look at it, the concept is better in all aspects, face, mechanical size, shirt, character mass. I think you have a strong concept there, just make that instead of redesigning as you go.
If i hadn’t seen the concept i would say, good job.
2¢
I love the hulk piece. Great work.