In this promotional shot, actor Heath Ledger is pictured seated at The Joker while Christian Bale as Batman stands behind him in a scene from The Dark Night, due out July 18.In this promotional shot, actor Heath Ledger is pictured seated at The Joker while Christian Bale as Batman stands behind him in a scene from The Dark Night, due out July 18. (Stephen Vaughan/Warner Bros./AP)

The first preview of the latest Batman movie, The Dark Knight, has resulted in profuse praise for the late Heath Ledger, who plays the Joker.

At the screening, reviewers also saw a note of dedication to Ledger at the start of the end credits. The 28-year-old Australian died in January from an accidental overdose of prescription drugs.

The statement includes a goodbye to special-effects technician Conway Wickliffe, who was killed in September in a stunt-car accident.

"In memory of our friends Heath Ledger & Conway Wickliffe," reads the tribute.

Early buzz from the preview indicates Ledger — who had a breakthrough role as a gay cowboy in 2005's Brokeback Mountain — will be remembered as delivering the best performance of his career.

"I can only speak superlatives of Ledger, who is mad-crazy-blazing brilliant as the Joker," writes Peter Travers of Rolling Stone magazine.

Travers goes on to proclaim: "If there's a movement to get him the first posthumous Oscar since Peter Finch won for 1976's Network, sign me up."

The latest instalment of the movie franchise, with Christian Bale in the title role, has the Joker crafting a series of abductions, assassination attempts, murders and bombings to lure Batman out for a showdown.

David Germain of the Associated Press elevates the young actor's portrayal of the wacky character above that of Jack Nicholson, who portrayed the Joker in 1989's Batman.

"Nicholson's Joker was campy and clever. Ledger's Joker is an all-out terror, definitely funny but with a lunatic moral mission," which the actor plays with "gleeful anarchy," according to Germain.

Directed by Christopher Nolan, The Dark Knight also stars Michael Caine, Morgan Freeman and Maggie Gyllenhaal.

"Heath created something entirely original. It's stunning, it's captivating. ... It's going to blow people away," Nolan said in earlier interviews.

With files from the Associated Press