Whoa! As a first post, i'm gonna keep this general. Your figure studies and life drawings recently have greatly improved since the first stuff you posted - great job! Just keep at it, since I've also noticed your updates have been a little sporadic.
Another great thing is you have much better tablet control, I can see your brush strokes are getting more confident and less wobbly. What I was gonna critique is the whole flat thing you were doing at first - but in your last painting you have more colour variation, which really helps with the value.
When you do stuff from imagination, try to use some reference for it, while there is improvement it seems like it would help you ease into the boundary between observation and imagination - my suggestion would be to do a still life or drawing from reference, then adding more imaginative elements to it, like some super awesome cybernetic attachments or something.
Keep updating, and I'll be stopping by again when you do *glare*