As said before, your traditional paintings are great.
Your pixel art still is quite lacking.
I think you could benefit from reading a few resources on color selection.
This thread on Pixelation was especially helpful for me (but image links seem to have died, it'll be harder to visualize): http://www.wayofthepixel.net/pixelation/index.php?topic=922.0
Anyways, I suggest, for starters, working on a big canvas, filled with an interesting background color (not white). You only use a small part of it, sure, but giving yourself room to paint means better art can be made.
Now, the reason I say not to use white is because colors in a scene tend be based around a background color, and if it's bright white, it's very annoying to decide things.
It also seems like you're making things too small. Try using a bigger brush, make that like a 2x2 or 3x3 pixel brush (make sure it's still pencil tool though) to blob in some colorful shapes. Then go in and refine those shapes afterwards by carefully cleaning up outlines and curves.
Taking a different workflow has helped me with my pixel art, at any rate. Hope this helps you.
EDIT: Here is a something I whipped up, that you might find helpful. (I'm just linking, so I don't completely derail the thread and confuse people who are scrolling through this): http://bananattack.com/stuff/art/pupuuship.png
Granted, it's not perfect since I only spent like 30 minutes, but it'll give you some ideas about how to approach pixel art maybe.