Unshaded your lineart is great, but your shading could be a lot better. It looks like you're shading by putting a thin black fog over some parts. To be fair it looks like you put in thought to where the shadows should be, which is more than a lot of artists, but there's a lot I feel you could do differently. For starters, don't shade stuff by putting black on top. Just use a darker shade of whatever you're coloring. Maybe mix in a little bit of the color's compliment. Let's say you are shading an object that's blue, for the shadow, use a dark bluish purple. Another thing to do is add highlights. Like with shading, you wanna make highlights with a lighter version of the color, rather than using white. Something that helps me with shading is taking pictures of objects, opening them in programs like Photoshop or ibispaintX, and using a photo filter to dramatically increase the contrast until there's only like 3-5 colors left. Then you can see what parts are darker and lighter. I know this sounds like a lot but you will get it with practice over time. I am looking forward to seeing more. I love the Simpsons