Six-hour Pullman adaptation is a hit, but it's too long for some

With an impressive cast, a production budget of nearly £1m and a script based on a trilogy of best-selling novels, it had every hope of success - even before the critics were allowed to see it. But despite the fact that the National Theatre adaptation of Philip Pullman's His Dark Materials at the National Theatre has sold out until the end of its run on 20 March, previews of the play, which stars Timothy Dalton and Niamh Cusack, have not been a hit with everyone. In two parts and at more than six hours, some children are finding it too long.

After a number of technical problems and cancelled previews before Christmas, critics were finally granted access to the production, yesterday, but they were preceded by a number of performances in December. And while most families have emerged full of praise, some found its length - and content - a bit much.

An usher at the theatre said some people had even left early. "People have left because they were bored. In particular, people from abroad have found it harder to follow." Another said: "I think if you're under 10 it's going to scare the pants off you."

But a poll of children and parents leaving two preview shows last week gave it the thumbs up, though some admitted there had been some squirming on seats.

Now it has opened, some children have also complained about its "frightening" representations of mythical creatures, including harpies, flying witches and daemons.Alex Veale, 12, and his brother Robin, 10, who travelled from Reading, described it as "loud" and "scary".

"It fits the book well: when it's scary in the book, it's scary in the play," said Charlie Mondelli, 10, from London. "If it was a movie, it would be scarier than Harry Potter." David Booer from Dartford, Kent, was equally enthusiastic. "It's all great," said David, 11. "It's frightening, but exciting frightening, not bad frightening."

The play, like the books in the trilogy - Northern Lights, The Subtle Knife and The Amber Spyglass - has already drawn criticism for its blasphemous message, especially as the opening coincided with the Christmas period.