There are so many variables to look for, don't the different sites offering free fonts have some kind of review system where you can get hints on whether a font is good or not? (The problem might be that people who just use the font in PowerPoint for their birthday poster might think the font rocks, while it lacks glyphs essential to the majority of the world.)
Maybe that is what would be needed, a community based review system for free fonts? Probably needs to separate technical and readability issues from aesthetic issues. I think making a complete check of a font would take many days of work. Just checking that all the glyphs are in the right places probably takes a couple of days. Then checking kerning tables and things like that.... /Peter
