I like to think of games like food. Everyone has different tastes, and there are rarely simple guidelines that will satisfy everyone. The guidelines that do work most of the time tend to be fairly trivial (e.g. “don’t eat moldy things”). Otherwise, it’s a complex art. So instead of looking for “guidelines” and rules for “what makes a good game”, I think it’s more helpful and productive to try and understand the “big picture” of the game design space. This means learning about all sorts of game design philosophies, some of which you will like and some of which you won’t. This also means trying to get an idea of how many people in a given market like what kinds of designs. If you’re going for mass market, you should probably design with the pieces that seem to appeal to the mass market (WoW, FarmVille). But if you’re OK with a smaller market and want to focus on a genre that you’re personally interested in, then it helps to understand that space as well and how it fits in with everything else. These are all things you can discuss and learn about, and I think as designers, we absolutely should so we can explore the design space with agility.
And the most exciting thing about video games right now? There is so much of the design space that we haven’t explored. Just look at how many awesomely creative indie games come out every year!