I just read this pretty cool article (free reg required, use bugmenot.com)
http://www.gamasutra.com/features/20050520/cifaldi_01.shtml
one of the conclusions of it is that the way to be a good game designer, is to just design a lot of games. I think this is very very true. Ive designed a fair few now, some were ok, some were bad, some are great :D but its only by going through the full process many times you really learn.
Maybe this is why we have so many bad games these days? Games are taking longer and longer to make, so the number of titles under the belt of the average designer is probably really low now?
just a thought...