If you liked the first Sherlock Holmes with Guy Richie's quick cuts and hyper reality set against the cold European post-industrial revolution *breath* you'll love this one.  Immediately you will realize he's taken everything and cranked it up a notch.  The plot twists intermix with the action perfectly but you will have to pay attention so you don't get left behind.  Fair warning, an older crowd may find all the density in the story difficult to follow.  Luckily, there are plenty of places to jump back on the train and there is enough exposition as the pace slows toward a climax to tie up your lose ends.
Robert Downy Jr. shines as much as ever and Jude Law plays the straight man with vigor.  Both characters keep their familiarity, though I'm surprised that Richie took the time to develop their characters just as much if not more so than the original.  Jared Harris also carries out the bidding of Holmes' legendary nemesis Moriarty well.  The character's ingenious intellect has always given Holmes trouble and this script continues that tradition with devious grace.  A lovely addition to the plot is Noomi Rapace who you may recognize from the original Girl With A Dragon Tattoo movies.  I don't know that her character was too much more than window dressing but she made the living room shine.  She plays a gypsy, which I would think would be difficult for a Swede.  It turns out she has roots in Spain as her biological father was a Spanish flamenco singer.  In any case, she shines and gives the movie another dimension so that it doesn't feel too familiar. 
It keeps you guessing and when you're not ducking for cover and allows you to soak up another dimension to the mythos of Sherlock Holmes.  I over heard many a pleased audience member talk about how it was one of the best of 2011.  My wife thought it was great fun, entertaining for the whole family.