Daniel Day-Lewis' gives such a commanding performance as Abraham Lincoln, he effectively makes the viewer forget that this is an actor, playing a role. As a movie about one of the most significant events in history - abolishment of slavery in the United States - it brings forward the amazing nuances of the actual event - the balancing act between just ending the war, and ending the war with the abolishment of slavery, the horse trading required to get the action done, the archaic positions put forward by those who oppose the abolishment (but thoroughly endorsed by the general public). It is a story about a man who seemed to carry all the burdens of the world on his shoulder - and still persevere.
And the movie is supported by a host of excellent performances - most notably by Tommy Lee Jones, Sally Field and James Spader. In terms of sheer amount of amazing acting performances, there is probably no other recent movie with such a great ensemble. It is a movie with a great script and amazing oratory (something missing from most modern political engagements). It is a movie definitely worth watching.