Uriel's got some funky light sourcing going on, his left arm and leg in particular. Both have shadows where the light should be falling on.
I'd suggest studying some anatomy, and especially some foreshortening. You don't have any fear of giving your characters some muscle definition, which is a good thing, but some study in the human form can give you a better feel for your characters. You can keep doing the style you've got going, but looking into some anatomy will make it even solid...er.
Perspective can also give your comics more depth; dynamic camera angles, structured backgrounds, etc. Plus, it's really easy to do, all you need is a ruler and some really light pencil work (or a line tool and a separate layer). There should be plenty of perspective tutorials online, so you can just Google'em.
My nifty link for this post shall be...
Save Loomis
This site archives the books of Andrew Loomis, a renowned (advertising?) artist from the twenties and thirties. They may seem outdated, but are still a prime source of information.
My prescription is one dosage
Figure Drawing for All its Worth and a minimum of five and a half hours of porning. Bring your sketchbook with you.
And don't bother calling me in the morning. I'll be...studying anatomy. <p>
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