The Ending (Spoiler)
Did anyone else think the fact that it was Irene pretending to be Russian could have been written more dramatically and, therefore, more effectively?
Proof comes when she produces the Omaha souvenir. It would have been more dramatic if it were not revealed by Irene. The revelation could have been unintentional or due to Harry's discovery of it.
The mystery of her true identity is the central plot point, but the film seems to just give it away, almost as an afterthought.