I've been using Google reader for many of my webcomics. However, with DD comics, all I get is BBcode from the users comments. Is there a way to modify it to show it correctly, or even the newest comic image?

Not as far as I know.
 
Basically you get a preview of the author comments and a link to the page.
 
I think the idea is that it gives you the barest info just to show you that there IS a new page so that you'll click on it and visit- meaning DD gets the ad revenue and all that.
 
But it WOULD be so much better if the BB code was rendered as proper HTML and the comic image showed as at least a thumbnail preview.