Andy Reid's weakness has always been in-game adjustments. He's a very smart guy. He can come up with a great game plan. He's obviously a very successful coach. The problem is whenever he hits a good coach or his game plan is not going right, he simply can't adjust quickly while in-game. And this is reflected in the play of his team.
I don't really agree. He is awful at managing games. Terrible clock management and his play calling is often terrible as well. He doesn't even try to adjust it either, nor does he seem to adjust it for the personnel he has, he just tries to run his plan regardless. Every so often he seems to try and get cute but it tends to backfire big time as it is often obvious (like one of the times they tried a screen with De'Anthony Thomas, the Packers could read it so easily).
On top of that he has a loaded staff and doesn't even use them. Brad Childress is on staff and would almost certainly do a better job calling plays/being OC, but nope. This way Reid can be lost with the game clock and calling plays.
He's really only had success when he has talented teams and good DCs who can give his offense breathing room. And even then Andy tries to gift the other team the game.
Reid might be able to be a good OC or coach if he could focus on one or the other, but he has blatant issues trying to do both, and it is ridiculous when you see the staff he has that he's doing both.