Thank you all for your entries so far! pepokish was sitting next to me as we looked through them, so these critiques are from the both of us in one go. If I fail to word her thoughts, I'm sure you'll see a post by her soon.
wizelsnarf: First of all; humanoids are pretty rare in Elements. I think I see what you're going for, though, so here goes! You mentioned it yourself already; it looks quite flat. There's actually a few reasons we can trace this back to. The main part of it, is the lighting. The figure is lit from at least 3 different angles; from the bottom left on the face, from the left at the left arm, and straight from the front at the upper chest. Using a consistent lightsource would help a lot in defining the features more.
When it comes to defining features, light always follow the shape of an object. Let's take a closer look at the hood of the character. It seems you tried to use the Gravity mark as a lightsource, with the hood casting a shadow onto the face. If you'd pull it off, that'd make for a very effective way of adding depth. The problem, however, is the light. Should the lightsource be the Gravity mark, then I'd expect a rather strong highlight on the cloak, which'd obscure the face a little, with a less intense highlight on the left of the face, following the curve of the cheek and chin and gradually fading to black. If this is a bit much to take in, please tell me, and I'll do a paintover when I get back to my own PC with Photoshop on it.
FInally, the composition you're using is fairly dull. A good part of this is the crop; cropping a character at the knees is a very traditional mistake, that'll make the character pop out a lot less. I'd suggest extending the canvas a little, there. Also, don't be afraid to hide things! Right now, everything is very visible. Play with light, with overlapping, and make some parts less visible to give the character a more unique look.
I'm eager to see what you'll come up with!
Ajit: For a sketch, this isn't bad at all! I'd give you the same feedback as ArtCrusader here, though: Try and define things more, and play more with a wider tonal range. I personally see a greenish Area 52 creaturew in a dress, but pepokish, for example, saw a plant growing out of a treestump. It's key to get some defining elements in there, that really show what the figure is. Don't be afraid to start working with a stronger contrast; you can always blend in things a bit more if need be, later. Your manipulation work already shows that you know what you're doing when it comes to values, so try and apply that knowledge here.
Krava: With your current sketch, the figure is a bit flat. I think if you'd try to add some more perspective to it, you'd get a much more interesting look. Imagine the critter in 3D space, and adjust the view about 30 degrees to the right; see what you can come up with. Like with wizelsnarf, a little more overlap could work wonders compositionally. When you start working out the sketch, I'd strongly urge you to add quite a bit of detail to the 'transition'area. It's the most awkward part to look at, so try and make it as sensible as you can get it.
Alright, that's all for now. Back to sketching, and I'm very curious to see what you all come up with!