The Design of Everyday Games analyzes Advance Wars and what makes it so much fun to play, even with older technology and gameplay.
The argument is that Advance Wars is incredibly rich and yet is not complex. You press a single button to do almost any action, unlike some games that have a different key mapped to do even the most similar things. Advance Wars is enjoyable, has plenty of variety, and yet doesn’t require too much brain power just to interface with it. You don’t have to think too hard about what physical action to take, leaving you more brain cycles to concentrate on playing the game.
There isn’t a focus on the engine, either. The game is more or less the same as it was when it was first released, and it is still fun because it was improved. It didn’t change drastically to allow for the latest tech. The game dictated the tech needed, not the other way around.
If your game isn’t as good as it should be, maybe you shouldn’t be asking yourself what you can add.
Maybe you should be asking yourself what you can cut.