For much of the cinema’s history, the movies have had the good sense to keep Sherlock Holmes’ nemesis Professor Moriarty off camera, an unseen menace made all the more menacing by his absence.

Guy Ritchie’s “Sherlock Holmes: A Game of Shadows” puts the infamous Professor M. face to face with Holmes. They parry, trade threats and play chess. But as the evil genius is played by the unimposing Jared Harris (“Mad Men,” “The Curious Case of Benjamin Button”), you can’t help but wonder why Robert Downey Jr. doesn’t just dope-slap this shrimp and “crack on.”

It’s not a fatal case of miscasting. “Sherlock Holmes: A Game of Shadows,” is still a romp, albeit an overlong one where the rompers romp at the point of a bayonet. But Hitchcock’s maxim — “Good villains make good thrillers” — holds true. And since Ritchie burned through his best bad guy — the cunning, cutlery-faced Mark Strong — in his first Holmes film, it’ll have to do.

Downey is more Chaplinesque, more whimsical and more English in this sequel, a two-fisted howitzer-barreled blast that manages to be lighter, funnier and yet more violent than the first Downey-Ritchie Holmes film. Check out the face Downey pulls when Holmes realizes that one leg of his cross-Europe pursuit of Moriarty will involve riding on horseback.

“They are dangerous at both ends, and crafty in the middle,” he quips, though he’s already landed his laugh with the look on his face.

Holmes is about to lose Watson (Jude Law), his perfect foil and bantering partner, to matrimony. And botching the stag party and almost ruining the wedding itself won’t be enough of a sendoff. It is “our last adventure, Watson. I intend to make the most of it.” That entails derailing the honeymoon.

Holmes has pieced together the puzzle that is the powder keg of Europe in 1891, and all the fuses lead back to the megalomaniac Moriarty. An age of anarchists, Cossack assassins and a new military-industrial complex raises the stakes.

Ritchie takes his Sam Peckinpah slow-motion violence fetish to artful new extremes and treats us to more scenes in which Holmes’ peerless powers of concentration and perception give him an almost supernatural ability to play through the variables in a coming fight in his mind, before actually martial-arts-ing his way past legions of evil henchman.

Downey and Law click like a polished comedy team, with Law more than holding his own with Downey’s hilarious excesses. Downey makes us believe that this “manic” (Watson prefers “psychotic”) detective is living on “a diet of coffee, tobacco and coca leaves.” It’s a role informed by the actor’s street cred.

Noomi Rapace ably leaves her “Dragon Tattoo” behind as a gypsy in search of her anarchist brother, who is mixed up in Moriarty’s plans. And Stephen Fry vamps it up as Holmes’ starchy Oscar Wilde-side brother.

If only the recycled Bond-film gadgets and Bond-film plot line didn’t weigh “Game of Shadows” down. If only they’d spent the cash on a bad guy with stature, instead of taking that phrase, “the banality of evil,” so literally. Playing this “Game” might have been even more fun.

Film focus

WHAT: “Sherlock Holmes: A Game of Shadows

RATED: PG-13 for intense sequences of violence and action, and some drug material

RATING: 2½ stars

Jared Harris, left, as Professor James Moriarty, and Robert Downey Jr., as Sherlock Holmes, appear in a scene from “Sherlock Holmes: A Game of Shadows.” Moriarty, who has loomed as the grandfather of all super-villains, is played with cool, quiet, chilling detachment by Harris.