Try to be more professional with your presentations. I know some of these are just your sketchbook pages and you're writing whatever comes to mind which is fine, but if you're going to show these as a portfolio and ask for professional critique (not that i'm a pro, but you should practice for when pros do see your work), there shouldn't be vulgarities scribbled among the drawings. It's not a huge deal, but it does reflect your character which plays a big part in who gets hired and who doesn't. Some probably wouldn't care less about it, but it's better to play it safe in this case for those potential employers who do.
Anyways, I think you know what the problems are for many of these, and there's only one way to fix them. Study. Practice from reference. Study anatomy. Study form. You have a long ways to go but the foundations are there; just keep chiseling away. I'm sure you're doing that already, but there's not much else to say for most of these sketches.
The body laid out in the grass: The grass is way too saturated, and it should get darker as it goes away from the fire. And where is all the light coming from? I only see the fire. You'll need to completely redraw the values on this, keeping in mind where your light source is.
On the first environment I actually kind of like the color scheme and some of the detail that the texture has created, but at this point it only weakly disguises the fact that there is no form here, and no attention to the composition of specific elements: the river is an awkward blob, the land is out of perspective and the background is just a pile of mud. Describe things when you draw. Implication is fine, and often plays to your advantage, but you stopped far too short here. The second environments suffers for the same reasons only moreso.
The foot is your best drawing. The part where you tried to erase the highlight in looks messy, but aside from that the lines flow well and reinforce the form of the shoe.
First off, I agree with Liffey regarding the vulgarities-- you should kick that habit right now. Remember that in the fields of illustration, concept art, etc... a lot of art directors will cross reference your name with your online presence-- even read some of your posts to get a sense of who they're dealing with. Just something to keep in mind.
Regarding Liffey's comment about the saturation-- your photo does explain your approach better, but one very important thing to remember about representational art is that it has to READ. Meaning, if you have to explain it, you've already lost the viewer. This will be even more true as you move into the professional world, because here you're just losing a viewer-- out there you're losing business.
Dude, I feel like you're at the same point as me, or at least it seems that way to me. I'm also not planning on doing any hardcore professional work for a few years, and I feel like we're both just trying to get the fundamentals down right now. You're definitely doing great with these and I'm also glad to have seen how much progress you've made over time. It's really inspiring.
I really like the studies you've been doing and how much you've been experimenting; definitely keep that stuff up. One thing I'd like to see you do more of soon is illustration stuff (if that's something you're into). It would be cool to see thumbnails that develop into sketches and then into full color illustrations.
You're definitely on the right track with the fundamentals, just make sure you stick with this pace and keep working your ass off! Great work!