When the 1973 horror movie The Exorcist first came out, people in cinemas were fainting in the aisles and running for the exits. If you've ever seen the film, which was adapted by William Peter Blatty from his original novel, you will know why. It's genuinely gruesome, depicting, as it does, a 14 year-old girl who is possessed by the devil and proceeds to wreak havoc on her own sexual organs with a crucifix, whilst growling vicious hate-filled obscenities at the people around her. The Woman in Black this ain't.

I should therefore say this now: if you are made to feel even the least bit queasy by gory, demon-themed horror, this definitely – definitely – isn't the show for you. As with the original movie, I found the gratuitous and graphic sexual violence - both verbal and actual - inflicted upon and by a minor exceptionally unsavoury. But we are talking about one of the most iconic horror stories of the modern age, so most people heading to the theatre will know something of what to expect. Does that make it OK that we're still depicting this stuff on stages today? I think the jury's still out on that one.

In fact, this new stage adaptation from John Pielmeier – who took the book, rather than the movie as his starting point – tries to elbow in all the thrills, jumps and scares an audience might want from a bona fide Halloween show and in the process loses something of the tension of the original. There are absolutely some excellent stage magic tricks from illusion designer Ben Hart, and some of the most memorable moments from the film (Regan's head turning right round is a case in point) are masterfully created. But the pace of the script, which is sparsely written and features no relatable, realistic characters, feels as though it is simply trying to get in all the film's main gross bits, rather than create a play which works.

A mixture of screens and projections are used in certain moments to create a vision of the ghostly demon and the terrible shadows that torment poor Regan. It's these, along with exceptionally loud bangs, crashes and bursts of light, which really make you feel the demonic presence. Ian McKellen voices the demon with a fruity twist, perhaps inappropriately, but his disembodied voice is probably the most rounded character in the entire thing. Adam Garcia and Jenny Seagrove are both fine as Father Damien Karras and Regan's mum Chris, but though there is an attempt at backstory, their roles are see-through. Clare Louise Connolly fares better with Regan, managing to channel McKellen's voice very well while dealing with the awkward practicalities of the numerous stage illusions. Peter Bowles as the demon's nemesis Father Merrin cuts a stately, weary figure, but he has about three lines to say in the whole thing.

It is true that this show will absolutely make you jump and squirm and it does deliver on some of the titillating goriness of the original. Perhaps exorcising our desire for cheap thrills is all we're looking for at this time of the year. But The Exorcist essentially feels flimsy, a piece created for the sake of Halloween, with the express intention of making everybody feel very uncomfortable.

The Exorcist runs at the Phoenix Theatre until 10 March 2018.