I remember seeing this when it was released, new years eve 2008. I haven't seen it since then, but it still gets a solid four stars from me.
The story and acting were the things that stood out - even though visually I had a hard time visualizing Frank Langella as Nixon (and trying not to visualize Michael Sheen as former UK PM Tony Blair) I think the effort put in by the actors and director made it work enough to buy in.
The attention to Frost I feel is an important part of the equation - up until then he was not taken particularly seriously as a tough interviewer (obviously a reason Nixon agreed to do the interviews, as he thought he was weak enough that he could spin this to his advantage). Combined with the financial risk, this built up the background story that this was a high stakes exercise for both men.
I loved Nixon's line about Frost's shoes.