Weird-ass lump

I'm trying some painting program called [SAI] and oh god it's pretty damn weird.
I'm not sure how and where it differs from Photoshop, but it's a rather stimulating work environment. The shapes, the textures, the lighting just flow out naturally. The blending system is neat; the brush sliders seem pretty abstract, but I'm slowly getting the hang of it.
I might be using that program again for other stuffs, I don't know. If I had a pen tablet (I'm still using my old mouse), I'm sure it would be an orgasmic experience.