Some critiques:
The girl on the right... her legs seem wonky in two ways. 1) they're far too short. 2) they seem to be pushed back, like her ass starts in the middle of empty space.
Other than that, the proportions are quite good. Shading your comic this way definately works, and is probably much faster than the original attempt.
Nice use of shadows, both in the shading, and the shadows cast onto the background by the main characters. Also, I like how you did the smoke from the cigarette. One thing you may want to do is change that, in each panel... get something dynamic in there.
Having the two characters standing in exactly the same spot/stance is ok, but you want to have something more dynamic than just their eyes. Perhaps some hand gestures, definately something with their mouths (they should look like they're delivering the lines) and subtle changes like the smoke. People will notice that stuff.
That may seem like a lot of criticism, so I will say this; it's solid, and has a lot of promise. If you look through many webcomics, and see their humble beginnings, you'll note just how dramatic the improvements are (after time) with some of these comics.
Example:
My first comic.Three months later.Penny Arcade:
Their first comic.Something more recentMac Hall:
Very first comic.More recentSo what you can see in the examples above is a good illustration (heh, illustration) of how much some webcomic artists improve over time.
The best thing to do is peruse as many different webcomics, and as much webart as possible. Check out some Photoshop tutorials, learn to play with layers, opacity, and some of the selection/blending tools.
