What the heck, critique is always good. I'll be the first one to try your critiquing skills out. I'm not afraid of getting even harsh critique so no need to be scared that I might get hurt.
This piece irritated me from the very beginning. It was never intended to be a full blown amazing piece, it was just a small freebie for a friend to begin with... but since I like Riddick I kind of did more than just sketched something.
There is something seriously wrong with the poses though, even though I used reference, which I of course modified (as I always end up doing). I realize Riddicks legs are like completely missing and he doesn't exactly look very relaxed or comfortable, doesn't look like he'd be leaning against the sofa or whatever that is (added it later quickly). The muscles aren't perfect either, but that's because the reference I used was actually of two quite skinny guys... and since Vin Diesel certainly isn't skinny, I had to modify it freehand. The shirt on the police should have more wrinkles, it did when I started out, but they looked horrible so I erased them.
Now I'd like to get some comments on how I should've drawn it to look more natural. Other remarks are welcome too. Thank you!
http://www.sheezyart.com/view/1109060/
(click for full view of course ^^)