Jeez, you learn fast! The first ones were already very well composed, but the last two show some very advanced posing and color work. Very impressive!
I really like the hair of the female character, the crouching pose of the last one, and the use of color gradients in both of them.
One feature you haven’t played with yet is line color. You’ve got a lot of the advanced techniques down already, I think you could have fun if you tried using different line colors here and there.