I do like your picture...and here's three easy ways my 'like' can blossom to a 'love'.
1. Shading and highlights. Since you did shading on your other drawing, you know what I mean, so that's basic.
2. Line weight: 'line weight' refers to the thickness of a line. Oftentimes, line thickness relates to light source...like, Mr. Rex's right arm: there's really no reason those lines should be so thick.
3. I'm repeating myself, but use an app with layer support. If you're going to go digital with your artwork, you might as well take advantage of what computers can offer. You seem like me and love dark lines (cartooning); therefore you don't want to hurt your line work. Drawing on a top layer and coloroing/shading on lower layers allows you to do just that!