Thanks for mentioning the lines and shadows. The lines, I find can be hard to get 'perfect' at times, considering how thin they are along with doing the colour underneath. And I think shadows give the image more depth, like how it's only used in the show to add impact to a certain scene.
Yes. Shadows are important. I love it if we can see shadows in the show. Especially in the new episodes. I think it just looks so, professional. And more detailful. It's different than in the earlier episodes. That's one feature which got the newier Simpson-Episodes. Lines are also important. The lineart is one of the most important thing in a picture. Btw. You're welcome!