Bengals first opponent - Cleveland Browns with the mighty Colt McCoy at QB & Hillis at RB, the Browns are currently 25th in passing yards & 26th in total yards on offense.
Bengals second opponent - Denver Broncos with Kyle Orton at the QB helm & Willis McGahee at RB averaging 2.9 YPC, they're currently 22nd in passing yards & 27th in total yards on offense.
Bengals third opponent - 49ers with Alex Smith at QB & Frank Gore averaging 2.5 YPC, they're currently 28th in passing yards & 32nd (Dead last) in total yards on offense.
So after adding all three of the Bengals' opponents passing / total yards together & dividing by 3, you get a league average of 25th in passing / 28th in total yards.
I'd say that based on the level of competition so far, the Bengals defense haven't played anyone worth mentioning to put them in any elite categories & have to play the number on scoring team in the league this week. It's hard for me to believe that Cincy scores more than their average amount of points (19) & the Bills score less than half their average (37.7), that would have to be a 50% increase for Cincy & a 50% decrease for the Bills to get close (not going to happen).
The Bottom line: Cincy is going to lose.