The Gist: Sherlock Holmes is investigating a series of terrorist attacks in London on his own because his longtime trusted associate, Doctor Watson, has terminated their partnership in order to please his soon to be bride. Professor Moriarty, Holmes' archenemy, seems to be behind the attacks, and reveals that Watson and his wife are a target of his revenge plans against Holmes. This forces Holmes to enlist Watson's help one last time, which will take them on a roller coaster race throughout Europe, whose political destabilization is Moriarty's ultimate goal.
Sherlock Holmes: A Game of Shadows is the follow up to 2009's highly successful Sherlock Holmes. Both helmed by Guy Ritchie and starring Robert Downey Jr. and Jude Law, I'm hard pressed to find any flaws in either film.
One thing that's been made very clear in the last few years is that rebooting, remaking, revisiting, or restarting a beloved franchise/movie/character, really hinges on the vision of the director (see Nolan's Dark Knight trilogy or Abrams' Star Trek relaunch).
Apparently Ritchie and Downey Jr., and Law secondarily, are a match made in heaven for a Sherlock Holmes who easily appeals to our modern sensibilities.
The Bottom Line: Sherlock Holmes: A Game of Shadows is a really fun movie to watch, full of dramatic action but peppered with jest by a Downey Jr. who was born to play this role.