First of all, I´ll admit that the last image is an improvement (satch_pose_Final.jpg) over the first you posted (satch-newpose2.jpg). Well, some aspects got better, others felt a bit flat.
I´ll start with anatomy. Some details are pretty good but most areas are showing a dodgy anatomy. Specially in the biceps area and the neck. I´m not sure how much of it is due to the anatomy itself or the lighting/shadow. I´ll get back on the light later. The knuckles (specially the guy´s right hand) form a straight line, when they should be in arc shape (middle finger in a higher point). Thumb in left hand seems to be bending in a strange way.
Biceps are way too big for a guy with this muscle structure. Plus keep in mind that the bicep is pretty much a cylinder with flat sides (the most “rounded” area is pointing to the front in a relaxed position). The forearm looks (right arm) loos good, although the transition from arm to forearm lacks some structure (specially the muscle that arises from triceps and connects with the forearm).
The neck lacks some structure as well, there are some bumpy areas that look a bit confusing. Usually there´s a muscle very visible in the neck, sternocleidomastoid, which is the one that comes from behind the ear (from the mastoid cavity) and connects in the sternum and clavicle.
And then comes another volume, the trachea (which is well visible in your image).
Back on the hands, they looked better in satch-newpose2.jpg. His left hand looks like he´s pressing some strings and the right hand seems to be “in action”, they´re more expressive in this aspect. In the last pose, left hand is kinda floaty (plus some ao might help the contact with the diapason, same for the right hand though).
The shading in the guitar body improved a lot and it looks pretty cool now, some reflections are a bit strong to me and it looks a bit too clean, maybe it would be a good idea to add some dirtiness. I´ve seen guitars looking really clean though, so that would be a minor thing.
The pants are in my opinion the single element that´s killing most of your image. Wrinkles aren´t helping to sell the pose, since they´re not pointing to the rest points (specially in his right leg, the left has some wrinkles pointing the knee, that´s good). Check this picture:
Same happens in most areas in the shirt. The strap should generate a good bunch of wrinkles pointing in the direction where the strap is dragging the guy´s shirt. In the shading department, the bump is way too strong (in the pants), and in the case you want to portray a very rough leather, you need to work the specular. There´s definitely something that makes it look closer to plastic than leather. Perhaps the problem is that this type of leather as a less focused specular and even more glossy reflections.
The hair in the arms look better in satch-newpose2.jpg in my opinion. In the final pose, it looks too thick I think, and they don´t seem to proyect any shadows on the arm, and that might make it harder to integrate (in case you render your char and the hair in different layers). Most of the white hair looks good though, I think we should see more of that in the face, not so much in the head.
Finally the shoulders, they seem to be smaller than they should, and even if he´s skinny, normally we should see a harder curve (from the acromion:
to the spot where it “meets” with the bicep).
I liked the lighting a bit better in satch-newpose2. I think it related better with the background. The thing with the final pose is that some areas look way black and in some spots (like under his nose, right arm bicep) it looks like it´s not casting shadows (it appears to be reaching the ear, and mixed with the light coming from the left of the image, makes a bit confusing surface). Plus the light coming from the right of the image could help if it was more blue (maybe it is though, and it blends greener mixed with the skin shader).
The skin shader, looks ok in some spots, and in others (again, right arm bicep) has too much scattering. The pose, he looks more focused on the playing in satch-newpose 2, that was a good thing I think.
Shading on the strap looks great (hey, that seems to be a good shader for leather actually!). Details like veins on the head are great, tendons and veins in the hand look very good too. I like the fact that his face does not look generic (even though in the other images I could have some crits for the face as well), he does have an expression with attitude, I think that´s a great thing (plus his lips seem to be asymmetric, it might be the camera angle but still it adds a lot of life to the character).
Sorry, the post got too long too fast! If I may add, just keep in mind this in only my opinion and it´s been laid out with the best intention. At the end of the day, you´ll be the one calling the shots in this image and maybe a comment or two could help, but it´ll be up to you. Maybe you don´t agree with any of this and that´s fine.
I hope I could be of some help!
PS: my english is not great, so sorry if I wasn´t very clear wording some concepts.
