Based on short, and not-nearly-exhaustive research, I used logic to address this question. I looked up the reviews for an adventure game that was pretty horrible, and had zero replay value. So, just to be clear; assuming the game really has zero replay value, lets see how they rate replay value.
They gave replay value a 6 out of 10. Therefore an 'average' game would be an 8 out of 10.
Even then, I expect that an awesome game would really be more like 9.5, because they'd nit-pick to make it look like a critical review.
Don't take my word for it. Take games that you know were absolutely horrible, and games that were positively excellent, and try this yourselves. [You should have done this anyway - trust but verify!] I'll be very surprised if you find any game scores less than about 5.5 - that should be a game that physically assaults you right out of the box.