Even something without gameplay can be greatness, which is something that Swords & Sworceries proves very well. The game has to attract you, pull you in and shake you. If it does that you're golden; how it does that is not determined by rules you can set in stone. It might be through great gameplay, it might be through creating an interactive world that makes good use of graphics and audio to define the gameplay (Thief series for example), it might be by telling a gripping story.
It might also be by making you shit your pants. Slender - I just can't play that darned game!
Fun is the key and the only key IMO. A game has to be fun.
BTW: congrats on your achievement