Based on a real story: The man's name was Alan Turing ...

Rating: 1/10 (3 October 2015)

and he worked on breaking Enigma at Bletchley. There the reality ends ... apart from the great emphasis on his sexual orientation.
As I am sure many people familiar with actual history have mentioned, the Enigma was broken in the early '30-s at the Polish Cipher Bureau. Turing's work concerned extending that to the enhanced Enigma introduced at the start of the war. Without the work of the Poles (which they handed over on the brink of the German invasion) the Bletchely crew was unlikely to have been able to make headway, and certainly not in time for it to be useful.
In any case, Turing's most important work (compared to which Bletchley pales) is his seminal work on computability theory. His paper, together with those of Kurt Gödel produced an earthquake-like shift in understanding the foundations of mathematics and what could or could not be proved or solved.