Well, thanks to everyone for the constructive crits!
@ PermaNoob : Your painting looks like a blissful dreamhouse, the type I want to live in forever!
I never really appreciate the difficulty of making a digital painting until I tried to do so myself recently as part of my class assignment. The Wacom tablet is the worst enemy in my life now, seriously.
When I had to do a digital painting of the sphere from a monochrome photo ref, my sphere looks like some black-white meatball that's soft and fluffy. It's hard to control the pen as it is (my digital drawings are very shaky and look like infant's scribbles), and painting digitally is worse.
Did you get accustomed to the tablet the first time you tried it? Or did it took you weeks / months of non-stop training?