George Lucas took his 1999 Star Wars sequel off Fox's books and paid for it himself, giving us Jar Jar Binks. United Artists believed so much in Michael Cimino's Heaven's Gate it bankrupted them when it flopped.

As much as we rail against the interference of studio suits and development executives who wouldn't know a decent script if someone rolled it up and shoved it up their arse, history is conversely replete with examples of directors given too much leeway and money who really needed reigning in.

But after the titanic box office of the original film and the amount of clout It gave director Andy Muschietti, Warner Bros certainly weren't going to tell him what to do besides 'here's eighty million, please do it again!'

Although to be fair to Muschietti and screenwriter Gary Dauberman, it's a fairly thankless task to bring an adaptation of such a huge novel to a close. First time around they got to pick and choose how much of the kids' story they told, and this time they had to cram everything else from the book in.

But Dauberman has made some horror movies (Annabelle Comes Home, The Nun) that are light on their feet no matter how critically received, so you'd think he knows how to trim a large book. Although in this case, it feels like Muschietti's edict was to include everything possible, from the iconic Chinese restaurant scene to the final showdown where Pennywise is part giant spider.

It's 27 years later and the members of the losers club who've left Derry have not only become successful in their fields, they've gradually forgotten everything that happened to them, an effect of Pennywise's dark magic.

But after a vicious homophobic attack at the town fair that sees him return to Derry to dine once more on the town's kids, Mike (Isiah Mustafa) – who's stayed behind and works in the library – calls everyone up and reminds them of the promise they made to return and finish him.

The grown up losers converge on Derry – Bill (James McAvoy), Bevvie (Jessica Chastain), Richie (Bill Hader), Ben (Jay Ryan) and Eddie (James Ransone). Stanley, as you know if you've read the book, can't face it and meets a different fate.

The actual plot of them trying to seek out and do battle with Pennywise (Bill Skarsgård) is too long to recount and frankly it's not all that interesting, lurching from one set piece to another with no real rhyme or reason and with the scares only existing because Muschietti thought they were cool, not because they mean anything.

However, the biggest problem the movie brings into focus is actually from the book, although it's not nearly as pronounced there. The monster ultimately makes no sense. If it wants to kill them all and can shapeshift and manifest anywhere, what's it waiting for? And, as happens in the restaurant scene and Bevvie's old apartment, it seems only the gang can see Pennywise and his effects. Does that mean he doesn't really exist, that's he the result of psychoses from the various abuses and neglect they all faced as kids?

For such a long movie, clear rules are never established or adhered to, rendering any running away or screaming (or the audience being afraid) kind of redundant. Even then, where there are scares, a few too many of them are cut off at the knees by throwaway gags.

Other problems start to stack up immediately. The guy playing Mike chews the scenery way too much and and the rest of a top notch cast often looks uncomfortable. I don't remember the Native American subplot about how Pennywise arrived from space from the book, but here it feels tacked on and throwaway, just first-pass story construction to try to bring very disparate threads and set pieces together.

None of it's very sophisticated and there's absolutely no depth. I barely remembered (before I watched a few YouTube videos) how much of it is taken up with them finding their artefacts, things personal to them Mike needs for some ceremony that will kill Pennywise for good. But it all takes almost three hours to get where it's going and badly meeds a trim. Finally – a common problem with Muschietti's films going right back to Mama – there's so much ropey CGI at times I thought I'd wandered into a Marvel movie.

I wasn't the biggest fan of the original film, but I hope when Stephen King books get their period of being hot all over again the new reboot is handled with a bit more finesse than this.