Well, they are just sketches and practice pieces. And you seem to have gotten a style down. So not much to say on that. You did say you were working on line-art specifically. I don't see anything wrong with the drawing outlines. But again, they're just sketches. You should try drawing a single picture of something and clean up the line-art/outline to make it look less like a sketch.
Personally, I think your generic class character designs are neat. They're not plain, but not too complicated either. They all seem to have a variety of colors and fitting equip/clothing style.