Wow, wordy feedback here
Haven't seen your old works, but this style looks fine. Since the first link seems to be just an experimental try-out, I don't think there's a need to critique it.
Jack's picture looks really cool. I especially like the hands, but his right sleeve is really bothering me. Maybe more folds or add shading to the folds? But adding shading to the folds would mean you would have to add shading to the picture and that would be a total pain....
Kevin: Looks nice, like the details in the flexing muscles, but his deltoids in his left arm seem small compared to the rest of the arm. You need to bring the arm more towards the neck and have the deltoids curve under the shirt. Like the belt detail too.
For Francine, you've already heard how the eyes and hair were off. However, the expression is nice ^^
As for your latest work, yeah, the top guys hair is squished to his face, I agree. Also, try giving more form to the hairline. Try bringing the ear down closer to the nose to see how it looks. From what I know about the anatomy of the face, the ear is close to the eyes and the bottom of the nose.
For the second guy, I'd suggest cleaning up around the bottom of the eyes. He looks like he has bags under his eye to me, and since his eyes aren't drooped, it makes him look a bit insane or high... I'd also suggest centering it better. When drawing the face around the eyes, nose, mouth in a front view picture, remember to keep the distance between the border of the face to the eyes equal for both sides.
For the bottom guy, I suggest bringing down the ear again. Also, his shoulders look slumped, yet when you draw the rib area, it's in that curved position that indicates that he's standing straight. A bad contrast, makes his body look disporportioned from the pectorals down. I think the easiest way to fix that is have him slumping for this picture and make him stand straight in another.
I know it's a sketch, so sorry if a bunch of these suggestions are a bit... the only word I can think of is much. ^^
It seems you draw the eyes, nose, and mouth first, than give it a partial frame of the mouth, than give him/her hair (of course, there's a chance I'm wrong but from how prominent the eyes, nose, and mouth are compared to the light lines of the face and hair, it's just my assumption.) To improve the framing of the face, it'd probably be better to make the person bald and than add hair, so the hair will usually be more centered (being light with the baldness so it's easy to erase.) That's from personal reference in my attempts to draw anime ^^;;;
I'm no expert at this so sorry if some of the advice isn't helpful or makes things worse, but it's worth a try to improve, isn't it? :3
