Just what is the 'fanboy'? It's an overused term in the Internet-aware age where the geeks are now the ones making the movies and producers pander to the perceived devotion to a character or series, determined to be 'faithful' to whatever source material there is lining spare rooms around the world along with packaged action figures and Warhammer figures awaiting painting.

But in Hollywood, as the saying goes, nobody knows anything. The all-powerful fanboy might not exist in such numbers as Hollywood hoped. After much fanboy hoopla, Serenity didn't exactly light the box office on fire for Universal. New Line (along with most of the movie community) were shocked when Snakes on a Plane didn't wipe the floor with the competition.

You'd think Quentin Tarantino would have a much wider following – after all, he's the king of the film geeks. But after Grindhouse scraped back barely half its budget, it seems not even Tarantinies alone are enough to generate a profit.

So it's with some bemusement one considers the web of politics behind the scenes of Spider-man 3 (see what we did there?) Sam Raimi had no interest in the character of Venom – the alien parasite that behaves a lot like the One Ring to Rule Them All (by attaching itself to a host and making them feel strong while corrupting them). But producers – among them senior Marvel Comics executives – insisted due to fan's wishes.

So if the man with the most auspicious arrival in modern film history in Pulp Fiction doesn't have a following big enough to return a $50m budget, how much damage could be done to a Spider-Man movie by a boycott from Venom fans?

If indeed nobody in Hollywood knows anything, maybe it's just that they'd lined up so many licensing agreements the only solution was to chuck everything and the kitchen sink into the script.

That's what the on screen result feels like – so bloated with characters and subplots but ironically feeling rushed and not full enough, juggling so many elements it affords little but a cursory nod to many of them.

Like the Rings series the original was a dazzling masterwork of stuff we'd never seen before (a plot in an action film!) that hinted at bigger possibilities. The middle chapter expanded everything, gave us more to care about, told a continuing story instead of just cashed in, and sent the action into orbit. But the final act – although hanging onto the quality – just couldn't top its predecessor.

Peter (Maguire) and Mary Jane's (Dunst) fortunes have turned around. After her big break on Broadway the critics trash her and she loses her role, and Peter's feeling the love New York has for their webbed protector, basking in the glory even though nobody knows it's him.

But wickedness is afoot as Harry Osborn (Franco) fits into his late father's shoes to avenge his death by killing Spider-man. Then there's the alien symbiote that crashes to Earth destined to attach itself to Peter and turn him to the dark side (sounds familiar?). Then there's escaped crim Marko (Church) who stumbles into a suspiciously unsecured physics experiment and turns to sand.

And there's the new photographer after Peter's job at the Bugle, Eddie (Grace), who'll play a more dangerous role when the Venom parasite takes over him. And there's Peter's science colleague Gwen (Howard), flirting with him more than MJ likes. And there's...

You get the idea. Raimi and co have to cram all this into two hours, juggling all the subplots with at least five action sequences. Nothing would have been lost by excising at least one villain and several subplots, but as everyone feels it's Maguire and Raimi's last outing in the franchise, Sony might have ordered the characters for the next two planned instalments jammed into one before losing their bankable principals.

None of which is to say Spider-man 3 is a bad film – by a long shot. Still leaps and bounds above the quality of most other blockbuster season fare, it's likely one of the best times you'll have in the cinema for the next couple of months. It's just that with a bar set so high by it's own success, apparently-crucial fanboy baggage has weighed it down more than it deserved.