In what would seem to be a highly improbable trifecta, the Brad Pitt vehicle Moneyball was an excellent movie loosely based on a great book sort of about a team that was often, but not always a great team to be a fan of. There's of course a lot of modifiers in that statement, but good things don't always come wrapped with tidy bows on top...
With my having attended 20-25 of their games a year from probably 2000-2005, I can say the Oakland A's provided some amazing moments to watch and countless instances of exhilaration as well as heartache (with both being necessary ingredients of fandom (see: Red Sox circa September 2011). One constant on this team of frequent roster upheaval was General Manager Billy Beane and what certainly seemed to be his "smarter than the average bear" approach to building a team.
When the Michael Lewis book Moneyball came out, I eagerly grabbed it like most A's fans and found it to be a pretty phenomenal read. While on-base percentage as a holy grail was the concept generally taken from the book, really what Beane appeared to be doing was using an undervalued asset that could be stockpiled using the limited resources (see: $ for salary) available. The fact that it was on-base percentage wasn't really as important as the approach of exploiting the overlooked.
Either way... a team that provided some great experiences and memories for the fan and a fascinating book.
Now, after several false starts including multiple directors, the movie was made and hit the theaters. I had high expectations going in and not because I expected it to be entirely true to real life (in this case, baseball) or to have the exact book presented in a different medium, but because I was excited to see what was done was the material available. After watching the thing, I walked away a fan... already was a fan first of the team for certain reasons, then of the book for others, and finally the movie for still other reasons.
In many ways, my view of what made the movie so good were elucidated by two pieces from a couple of my favorite sports writers. First Joe Posnanski on his blog and then Austin Murphy in Sports Illustrated wrote about how the story told in the movie didn't necessarily stick hard and true to the events that transpired, but was both tremendously interesting and unlike almost every other sports movie ever made.
Excellent writing from each guy on a very cool film (again, which was pretty much on a great book for the most part about the building of a great team)...