I went to see it with a friend last Thursday.
Personally I think it was okay, not brilliant, but okay. They certainly did try to make it historically accurate, but several times strayed from history for dramatic effect. They exaggerated the chance of success of the plot after the failure of the assassination attempt (pretty much suggesting that it would have been successful anyway had it not been for the officer in the intelligence office decision on whose messages to pass on). The scene with Goebbels preparing to swallow a cyanide capsule in case he was to be arrested was also an invention for the sake of dramatic effect. Some people were, in my opinion and from what I read, presented in too negative a light. Most strikingly Friedrich Olbricht and Carl Friedrich Goerdeler were presented like they had done nothing but slowing things down and messing things up which Stauffenberg had done alright; I do not think this did these two men justice.
There are also some rather funny blunders. For example they seem to presume German church windows to be rather solid. We see a church with a bombed roof, but the stained glass windows are perfectly intact and in place (in fact most of these stained glass windows were taken out to protect them from damage when the bombing began).
During the scene of the execution of Stauffenberg, Haeften, Obricht, and Quirnheim there was the most striking case of visible movie equipment I ever encountered and I wonder how this one could escape the people in the post production office. Historically they were shot in front of a pile of sand, in the movie you could see that they had built up a wooden wall with sand spanning the whole courtyard of the Bendler Block. Everything, the wooden wall as well as the poles which supported this requisite were completely visible.
Still, the movie was not bad. They could have done better but it had been feared by many that they would do dreadfully worse than they did.