Nice stuff, I especially like the hand even though the knuckles seems to show to much for that angle. Earlier I wasn't so much referring to the number of colors as the strength of the colors. You tend to use very strong and contrasting colors, try working more with subtle nuances and use more subtle colors, right now they're all over the scale.
I'm really digging the hand holding the wine glass. the color and lighting is looking really nice with the highlights on the glass and the shades in the wine underneath. the line drawing looks more life like as far as lines go. so be carful to not loose those importnat lines and shapes when moving form line art to coloring. looking good.
I like it. It intersts me, however don't forget diegesis... your telling us about this creature, at the moment we can count maybe 2-3 major things from your concept. What im saying is I want to know more about this creature. The soultion may be to draw many thumbs and explore what the cow - heart haverster actually is, then pick out the defining features.
I think you have a really strong drawing basis. I really like your life drawings, because you have a good sense of the figure. One of my instructors once told me that I'm much better at drawing than painting because I've been drawing for much longer. So when I'm painting, I should start with a good drawing, and as a result my painting will be stronger because it plays off my strength.
I think the same thing may apply to you as well, so perhaps you can try starting with a really solid drawing first, and then painting on top of it. This may also help with your mushy edges, because your line drawing will help you define where edges are. Then you will know better where to sharpen the shadows. Don't be afraid to be really harsh with value transitions! Sometimes it also helps, if you use photoshop, to do all your darks and lights as selections at first. Grab that polygon or free selection tool and block in the light and dark areas. Then you can blend the edges together to soften the effect.
Another good idea is to always work in 300 dpi, and zooooom right in around the value transitions to get them nice and sharp.
Here, I did a quick tutorial about what I was talking about just because. It's kind of bad. Sorry But it illustrates what I meant. And you can totally see how I'm worse at painting than drawing -___-;; Nonetheless, I hope it helps. This is only one of many ways to help you get sharper edges though, and of course this is just advice.