Short version: If you liked the last Sherlock Holmes movie, you will like this one.
The plot involves the nefarious archenemy Moriarty (Jared Harris) secretly attempting to manipulate a world war in order to make a killing on bandages and ammunition sales, war profiteering at its worst. Holmes (Robert Downey Jr.) is still the neurotic super-observant bad boy with a penchant for self-destruction, made worse by his grieving over the death of his girlfriend. Watson (the ever-charming Jude Law) tries to live the upstanding life and manages to barely arrive to his own wedding worse for the wear after his Holmes-style stag party, but he is drawn to Holmes and his exciting life for one last adventure.
The rollicking, nonstop action scenes are stellar, with amazing slow motion effects throughout. This movie has it all: heavy artillery, gunfights, judo, fist fights, chases, swords - even the girls get to play. The gypsy woman Simza (Noomi Rapace from "The Girl with The Dragon Tattoo") shows she can sure hold her own in a fight; this character is reminiscent of Ziva David in the NCIS TV program.
This is a smart movie. The witty repartee between Holmes and the dripping-with-evil Moriarty, Watson, Watson's wife (very well done by Kelly Reilly) and about everyone else is terrific. Very pithy.
Robert Downey Jr. has made his mark on the Holmes character much as Johnny Depp has his Jack Sparrow; he manages to transform Holmes from a dry literary genius to a tortured, flawed action hero who somehow manages to land on his feet most of the time. The interplay between Moriarty and Holmes in their cat and mouse game is on screen charisma that cannot be pretended.
This is not Shakespeare, but it is a fun movie to be entertained with for a couple of hours. I give it 3.5 out of 4 Miners and offer this advice: Go see it.