I think the main flaw for Buffalo right now is still the offensive line. I wouldn't say it's a major flaw, but I'm not convinced yet that this is a line that can help get the yards when they're needed. The midsirection plays and Tyrod's feet help, but when it comes to straight-up run blocking I think they still have a ways to go.
Then again, I've always believed that it takes the first month for an offensive line to really come together, and on top of that, Roman's blocking schemes are supposedly very complex, so I'm looking forward to seeing them get better as the year goes on.