Suggestions on the art...
The backgrounds are usually very, very bare, when they're there at all. Some background would be useful. In the current strip, the speedster and Lightbringer seem to have no backgrounds at all. Backgrounds would convey a sense of depth and detail.
Another suggestion that's helped me---make a collage of images. Don't trace, don't lightbox, but putting together real images in your graphic program is relatively easy. I do that, print them out, and use them as reference to make my drawings from, and it seems to give them more "weight" and gives you a more realistic feel. Both google and yahoo allows you to search for images, and corbis is another good resource.
There are tons of good drawing resources out there, and many of them have helped me. Proportions, especially, need to be worked on. People tend to concentrate on the face, but for instance, in the latest Lightbringer, the heads are waaay too narrow, because you're concentrating on the face, and making it as large as you think it's important. But the head---the ears come in the exact middle of the face if you're looking at it from the side, and there is just as much BEHIND the ears as in front of it. In many of your drawings, two-thirds or three-fourths of the head is in front of the ears. That's a mistake a LOT of people make when they draw. You're not alone in that.
These are things I learned the HARD way---lots of my early drawings for Mindmistress are terrible---and I'm just trying to save you from the mistakes I've already made. And obviously I have a long, long way to go.
Just suggestions, okay? ---Al