Scorched Earth

Gameplay: 10/10
Graphics: 1/10
Story: I don't think it has one.

And that's why so many people played Scorched Earth, Tank Wars, and other variations. Remember the monkeys that stood on buildings and threw bananas at each other? Same thing.

Graphics and story are a bonus. Of course, an RPG with no story is generally crap, so it can differ from genre to genre.