Your tablet stuff is awesome, man. I, too, like the mouse dude. But, Question: what's with the sharp, jaggy part on the robot's arm?
Also, please, please, please don't start overutilizing brushes. I'm talking specifically about the one with the demon and the dude in the clouds/fog. Dude. Your clouds are probably like one of my favorite things about your art. That brush just ain't cutting it man. At all.
The lines on the aforementioned pic remind me of David's lines, you know? All contour-gesture messy-but-interpretable and shtuff.
Also, on the same pic, (again), I like the lighting on the hero-type dude, but on the rest of the scene it could be a bit more...uhh...powerful? More contrast on the demon and stuff, you know? More emphasis of form on the demon and stuff, yeah? That's why, I think, the lack of outlines doesn't work as well as it could. Not enough definition where there should be.
Err...sorry. Kinda got carried away.