I responded to a debate on Gamasutra about David Surman's presentation at the gameconference GameCity: 'Game Designers Are Undervalued' (David Surman is Senior Lecturer at Newport Art School):
"Game Design is a independent design desciplin that can be taught. It's a subset of interaction design, which have been around for ages. Anybody who wants to claim that they're de facto game designers should know at least the basics of interaction design & game design (Start with Rules Of Play). If not, then you're just a programmer/tester/producer/gfx artist with a new label on your business card (and likely to cost your company money by doing unessacary iterations or creating inferior products).
Game design (if taught correctly) is just as demanding as programming and the products are every bit as tangible as programming; - mainly as design documentation & creative direction during the development.
Unfortunately most of the game industry doesn't understand this as the usual way of doing things have been to promote selftaught employees to designers, based on their "ideas" (or more often: their trackrecord in other postitions in the company). Some of them have succeded, but the vast majority (around 99% of the projects) have failed miserably. Those that have succeded have done so through massive amounts of costly iterations. The whole idea of selftaught designers and that "game design can't be taught" should be obliterated from the games industry ASAP.
There's a huge difference between being able to tell if a existing game is good and whether a game concept (not an idea!, - a full concept!) is good. Good game designers are able to analyse how likely it is that a game concept will be a good game. A good game designer can scrap a design even before any documentation has been made and he will be able to tell you exactly what didn't work and why.
I know that a lot of people feel that they can do design based on their experience from other fields in the industry, but that's like believing you know how to fly a plane because you've been passenger on one".
The best designer would off course have a interaction/game design design education with added experience from the industry. He would also have to be a reflective practitioner.