The Big Short is about three different groups of hedge fund managers who realize that the housing market is going to crash several years before the big crisis. It follows them as they work on getting more and more money to bet against the mortgage interesting. It's fascinating and really sad the extent to which borrowers were scammed, and the indifference of the financial big shots involved.
The Big Short has a tense momentum. On one hand, you are kind of rooting for these guys who are going agains what seems the largest odds, and who weirdly seem to be heroes as they uncover the enormous flaw in the economy. On the other hand, they are going to benefit from the devastating 2008 collapse. This is mitigated by their growing cynicism and self doubt.
The movie is shot in a frenetic pumped up way that gives an otherwise pretty dry storyline more energy.