To people who say "it's a movie, not a documentary" I'd say "do you believe that Alan Turing's story was so uninteresting that it had to be padded out with extra drama?"
Spoiler (click to reveal)
Specifically the bit with the convoy being sunk and the suggestion that, to stop the Germans realising that Enigma had been broken, it was the cypher team that would determine what information would be acted on, using a mathematical formula.
Downfall comes to mind. Or The Revenant. Or Lincoln. Close enough to history where it doesn't interfere with my suspension of disbelief. The Imitation Game pushed too far over that line, at points, and enough times to ruin that.
I think the makers of The Imitation Game wrestled with key questions in writing and directing it, like: How do you make math and early computing interesting? Or how can code breaking be entertaining?
I guess I was expecting Sink the Bismarck meets Good Will Hunting or The Social Network. Something like that. A Beautiful Mind. It was almost there.