This highly reminds me of our countless hours playing that
online LEGO-like game.
I think you should justify your use of paint. You're not using a pixel matrix, its a painting canvas. Let the paint spread, let us see the paint strokes, and use your imagination to create, instead of simply copying the sprites. What you're doing is just like an oversized print of the sprites.
You want the pixels to be aparent, so that the 8-bits feel is kept, that's cool. But you can instead of using pixels, using paint strokes. Or give the images more life and less geometry. Remember the old atari and odyssey2 game boxes art? something like that but with good taste would be nice.
I recommend taking a look at Van Gogh for inspiration (ok, i'm not saying you should paint like Van Gogh, but if you can see the way his paintings strokes form an image you'll see it's highly connected to the pixels idea).
