Look at his iMessage screen comparison [1]: yes, the old screen looks a bit geocities, but you can actually read text very well; the new screen is almost unreadable. The prime aim of iMessage is to make people read text, not to look cool.
It doesn't matter if there are options to thicken the font -- the whole point of OSX/iOS UI was that you should not need options, because defaults should be good enough for most people. This is clearly not the case with what we've seen of iOS7, and that's a problem.