That's actually kinda a cool pose, I wasn't too sure about the bent knees at first and wondered where you would go, but this works. Only the feet seem too close to each other in the first pic making him slightly unbalanced.
See you made the backpack thingies also slightly different from the concept. Also, the shoulderpads are hugging the shoulders less?
His right underarm looks a little dodgy but I'd bet you've noticed that as well.

And for the weapons I'd actually recommend using different materials for both sturdiness and practicality. Like plasticard, rods or brass.