There is thunder and forked lightning above the Palazzo Ducale. The gargoyles are spewing water into the ancient courtyard. A monsoon is drenching Venice, and the midnight guests of the Doge are crammed into his ancient cloisters. You can barely breathe for the perfume and glamour. Casanova is back in town after 250 years in exile, and he looks remarkably like Heath Ledger ( pictured right). He has shaved his hair off in an effort to look monkish and inconspicuous, but it doesn’t work: those chiselled good looks are hard to hide, and legions of happily married women are trying to scrounge a kiss.

Jeremy Irons squeezes past wearing the 18th-century costume of the Inquisitor General. He is the villain of Casanova, and the scourge of serial seducers. He won’t be parted from his papal robes for love or money. Jeremy adores a good frock.

Casanova being a Lasse Hallström movie, it is dressed to heterosexual perfection. Ledger swaggers from sword fights to swooning damsels with the comic cool of Johnny Depp in Pirates of the Caribbean. He sports a floppy ponytail and some cracking one-liners, but the period film falls agonisingly short of doing the decent thing and going completely over the top.

I poach a seat on Irons’s boat back to the Lido. Here, the talk outside the famous Casino is whether Ledger can win a top prize for his performance as a gay cowboy in Ang Lee’s terrific film, Brokeback Mountain. With another starring role as an emotionally retarded scribe in Terry Gilliam’s frothy comedy, The Brothers Grimm, on offer, he is clearly the most confused actor at the 62nd Venice Film Festival.

Set in Marlboro country, Brokeback Mountain tells the story of two young ranch hands (Ledger and Jake Gyllenhaal) who spend the summer of 1963 eating beans and guarding sheep in lonely isolation. A freezing night sparks a moment of intense, belt-loosened intimacy in a tent. Days spent in silence are interrupted by snatched moments of need. The haunting grip of Annie Proulx’s drama is how the men fail to cope with these taboo moments when the summer breaks and they are forced to get on with the rest of their lives. Repression and jealousy gnaw away at the marital knots they tie with Michelle Williams and Anne Hathaway. The denial is heartbreaking. And the guilty romance survives, mostly as an itch the two men can only scratch when they meet for “fishing trips” at Brokeback Mountain. The performances are magnetic. The scenery is magnificent.

I am puzzled by the teenaged waif door-stopping the Excelsior Hotel about 100 yards away, holding a placard with the legend “Dear Mr Cronenberg, Spider is the best film ever made.” Perhaps it is a post-modern joke. Her friend might have better luck with her cardboard plea to sleep with Björk, who has the starring role in Matthew Barney’s latest piece of art house barminess, Drawing Restraint 9.

Meanwhile, George Clooney is stunning the punters with his black and white movie, Goodnight. And, Good Luck, a powerful satire about television news set in 1953. Clooney loves the festival catwalk. He suaves his way through the paparazzi. He waves at fans who have waited nine hours in tropical heat to welcome him. His film, too, is brilliant, and it bookends The Times bfi London Film Festival at the end of next month. In it, David Strathairn plays the vintage CBS news anchorman Edward R Murrow, the journalist who faced down Senator Joseph McCarthy and exposed the House of Un-American Activities as a sinister witch-hunt. Clooney is almost too good to be true as his harassed producer, Fred Friendly, but this film stings for all the right reasons.

The rhythm and pace of the television newsroom is cleverly measured against the stakes. William Paley, the boss of CBS (Frank Langella), is besieged by vested political interests. But Murrow decides to put the station’s credibility on the line.

The film provides a surprisingly “real” debate in a festival addicted to genre. Expensive and glossy fear is as much in evidence as celebrity. Scott Derrickson’s The Exorcism of Emily Rose terrified the living daylights out of me. Jennifer Carpenter plays the title heroine in a “true life” tale of head-spinning possession. But Calista Flockhart’s turn as a nurse in Jaume Balagueró’s Fragile — in which she pitches up at a gothic NHS hospital on the Isle of Wight to look after a handful of disturbed children — is destined to become a Rocky Horror staple for all the wrong reasons. The director’s grasp of English is obviously as tenuous as his grasp on reality. Among the incongruities on offer are a skyscraper lift-shaft drama which takes place in a two-storey building, and a scene in which Richard Roxurgh pumps the national grid through the toasted star in order to bring her back to life. I guess it has to be seen to be believed.

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