I had to re-watch Spy Game three times before I felt I got a complete understanding of everything going on. Brad Pitt also does an amazing job, but Redford steals the whole movie. In several scenes, but especially the scene on the Berlin rooftop, Redford gives a performance that is unlike almost anything I've ever seen in cinema. You almost get a sense that if you were to meet him in the street, you'd get someone named Nathan Muir playing the part of Robert Redford - the transformation is that complete. There are performances in this movie that defy description. While Spy Game is so fast-paced that it's difficult to keep up the first time around, I think that's what makes it such a great DVD. Then, years later, I got around to watching it again. I did end up buying it, though I was never sure why.
I made the mistake of only watching this film once the first time around.