Your art is fairly mediocre, but I've seen some great pencil pieces and with enough work you can easily put digital cartooning work to shame. Your problem is that you're not willing to spend the time that needs to be spent in order to make a piece great. You're going to need to go through every piece that you've done, every stage of the drawing, doing revisions and alterations - anything that needs doing, doing.
First of all, your lineart. This is want you want to concentrate on - coloured pencils look incredibly cheap, and using them for anything more then mild colour tinges (say, a hat here or a sword there) but in drawn artwork it's the lineart that sells the piece. You probably want to start off by going through sketch layers - that is, starting out with nothing more then positioning the characters, then basic body parts, then your details. That's just to get the lot underway, but because it's pencil work sketches are fairly easy to do and are quite expendable.
Secondly, you want to do some experimentation with lineart thickness - cartooning, you can go incredibly thick and it will hardly affect the picture itself, so go nuts. Firming in, cross-hatching, corner-work - all things that would be great for you to consider in order to increase your skill with the pencil, try and just master every single technique you can find - while it may not always help with cartooning, be assured that later down the line that you will want these techniques learnt, so learning them ASAP will help you get around the blockade.
You might want to try using ink, too. While canvas and general painting (those which make the artwork look "prettiest") may not be directly available to you, inking is always a good way to finish off a piece and that it's also great to make any pencil artwork look, well, great. Any perceived loss of detail is made up for in straight, binding lines, and an overall sense of finish to the picture. I've heard people complain that the loss of "texture" in the work when you're not using pencils at all, but to be honest it's not worth the loss of professional quality that you get when refusing to ink your work.
A few pointers, just to help get you in the right direction, whether you end up doing this type of work or this type of work, it's completely up to you.