Let’s be clear, there is no “one true game”. Everyone has their own preferences and tastes. Gaming is like anything else in this respect. That being said, I think there are aspects that make a great game. The ones that really standout have a special something that people really gravitate towards.
(Since this is a fairly large issue, I’m going to break this up a bit, and just focus on one little thing.)
For me, one thing I like in a game is one that doesn’t promote buying a ton of books. This is always something that makes me smile. A game that is just one book? Sign me up! I love this feature of gaming. I hate it when designers structure things around purchasing multiple books. It’s just really frustrating.
One my absolute favorite games is definitely 13th Age. The system rocks, and really, all you need is the core book. Absolutely nothing else is required. The core book has all of the rules for the game.
The Basic Fantasy RPG is another great example of this approach to writing an RPG manual. There are other examples as well, but the two presented here are ones I’ve actually played. I can say that they are both robust and quality systems. (The PDF of Basic Fantasy is free!)
What gets included into a book is just one thing to consider, but for me, its super important. I hate having shell out a ton of money to get a full experience for a game. I know it’s a business, but if the product is quality people will buy it.