Well yeah, start with the obvious, arm is too long. But somehow no one mentioned why. Stand up and arms to your sides, fingertips only reach down your thighs, right? With the high waist of your dude (covered by the shirt somewhat) your lovely young man has his fingertips at his knees, thusly gorilla arms and it looks off. Well, gorilla minus the muscle and what not.. and hair.. and whatever, you get what I mean.
Fold on the bottom of your shirt are too tight and remind me of the bottom of drapes which is why that's also looking a bit funny. Loosen up the folds only go for a couple. Also, if it's that loose on the front give more room on the sides as well to even it out.
You've got the loose fitting on waist and arms but the collar's sitting perfect on his neck, bring the shirt a little higher off the skin, it'll make it look less painted on. Even if you've got thin material (unless it's like lycra or something else plastic and sweaty) it should sit off the skin a little. Adds a bit of depth and what not.
I do like the shading and the depth you've done with the shoulder/arm/sleeves, especially on his left side. It's quite nice.
Jeans!
You mentioned in reply to one of the other posts that he's got tight jeans, you've got much too many fabric folds and in odd places for that. Wear some jeans! ..actually, it'd be easier to just google image some images of jeans, (tight fit if that's what your going for) and see just how things hang off the body and where creases and folds actually sit. Generally they're at the crotch/knees/folds from the cuffs/maaaybe from the belt loops. You should have mostly smooth unbroken lines along the legs themselves with all the texturing at the bottom/crotch.. and well, knees, but your guy's facing us so that's not going to happen so much and with tight jeans it's likely to be smooth with a straight leg anyway.
I'm not quite sure what's going on with the jeans at his ankles.. they're kinda bunching like slacks, though I'm assuming it's more they're ment to be bunching on his shoes, yes? Mn. I don't wear jeans in that style (yay flairs) so I'm not so familiar and can't comment so much.. bother. Like I said earlier, picture references are your friend.
His belt/chain thing hanging off his side needs a visible backing, as it's sitting it looks kind of cut in half. You should be able to see some of how it loops around his waist with how it's positioned and such.
Overall you've got a nice enough picture. It's all very serene and peaceful, calm sort of affair and what not. I like his face, can't find any faults with it (and that sounds negative, bother). Head in general's all good and yes.
Maybe a bit more of a dynamic pose next time.. Though reading the personality so far maybe that doesn't suit him so much? Still, even quiet people have their moments and compositions they can sit in to look more lively/interesting and what not.
Anywho, nicely done, not seen any of your other work so can't compare how it goes with your other stuff. Hope I don't sound too hard through that. I write long crits stating my opinion and such, so yes.
Hope something helped!
Draw more!
~WSP