For me, as a reviewer, a patch is either obvious, correct, and complete at first sight - or it is difficult. I can review only one difficult patch per week (currently), and that can easily cause patches that I need to review to stay in the tracker many months.
The problem for the author of the patch is that he/she doesn't know that. You may drop a comment like "please explain how to reproduce the problem / why the patch is needed / how your patch fixes the issue" or "the patch is complex, can't you write smaller patch or try to fix it in a different way"?
If Martin doesn't understand the patch, who will understand it? :-)
-- Victor Stinner aka haypo http://www.haypocalc.com/blog/