Look at the box office numbers that are coming through for some of the big blockbusters of the year, and you can't help but wonder if a sea-change is in the offing.

For the past couple of years, and for the next few as well, Hollywood has contented itself with primarily giving us a collection of sequels or movies based on previously-published properties. The clamour to make a successful franchise is obvious, and as such, the movies that are heading our way - with the exception of Inception, to be fair - have been adhering to one template or another.

However, over the past few weeks, the box office hasn't quite been going in the direction that Hollywood bosses would like. It started, believe it or not, with Iron Man 2, which opened to $128.1m in the US. Staggeringly, this was regarded as a disappointment in some places, in spite of it significantly eclipsing the $98.6m the original made on its opening weekend.

However, in the run up to Iron Man 2's opening, some were predicting we were looking at an opening weekend in the States closer to $140m. There was certainly a feeling that Twilight: New Moon's $142m should be within its grasp.

And yet Iron Man 2 fell just a little short of projections. Granted, part of that may be down to the fact that it arrived in Europe a week earlier than the States, and the reviews from this side of the Atlantic weren't overly enthusiastic. But even so, there was a feeling that there was a bit more love out there for Tony Stark than the US opening weekend amounted to.

However, since its opening, Iron Man 2 has rushed its way to a worldwide gross of nearly $600m and counting, and there's certainly enough in the bank to warrant an Iron Man 3. Paramount and Marvel are hardly sobbing themselves to sleep over that kind of cash.

Elsewhere, though, the story's not quite as upbeat. Universal, for instance, was looking for a brand new franchise with its fresh take on Robin Hood, uniting Ridley Scott and Russell Crowe once more in the process. A month after it's opened in the States, it's still not crossed $100m in takings, although a solid international performance has seen the film close in on $300m in total. Don't go expecting Robin Hood 2 anytime soon, though.

The pattern of underwhelming opening weekends has been repeated, too. On paper, Shrek Forever After's $70.8m US bow is impressive. But contrast that with the $108m opening for Shrek 2 and $121.6m for Shrek The Third, and it's a disappointing number. Shrek Forever After's US take is standing at $210m right now, and again, while that's a lot of money, that's over $100m less than its predecessor in the US alone. The Christmas 2011 release of Shrek spin-off Puss In Boots has suddenly got a bit more work on its paws.

Sex And The City hasn't been immune, either. Most of us had this one marked down for a massive hit, guaranteeing SATC3 in the process. Yet, while a third film is still likely, expectations are likely to have to be dampened. Sex And The City 2 had an opening weekend in the States of $31m, a far cry from the $57m that greeted the first movie. It's currently sitting at an $84m US gross, and again, it's the non-US box office that's turning it into a bigger-than-otherwise hit.

Non-sequels haven't been doing much better. Disney's attempt to kickstart a Prince Of Persia franchise look over given that Prince Of Persia: The Sands Of Time - an expensive Jerry Bruckheimer blockbuster, remember - has banked $72m in the US to date off a disappointing $30m opening weekend (overseas has kicked in an extra $190m, which should point the film towards profit).

Fox's talking animal family movie Marmaduke opened to just $11.5m, Katherine Heigl vehicle Killers generated a $15.8m opening weekend, and even the comedies are suffering. Get Him To The Greek, for instance, took $17.5m in its first weekend, but that's a long way ahead of MacGruber, whose pitiful $4m opening US weekend has killed many Saturday Night Live movies for years to come. There seems to be little sign of a comedy breakout hit of the ilk of The Hangover this year.

Perhaps the biggest surprise has been the tepid performance of The A-Team, which has had its backside handed to it by the remake of The Karate Kid. The A-Team has racked up just $26m in weekend one against $56m for The Karate Kid, and it can't help but leave you wondering what's in store for the films ahead.

In the weeks ahead, you'd only mark Twilight: Eclipse and Toy Story 3 with any confidence as big hits. But what now of Tom Cruise/Cameron Diaz vehicle Knight & Day? Suddenly, that's looking like a massive risk (although one that may work simply because it's one of the few films relying on star power over any form of franchise). The Predators reboot, likewise, will have a fan base built in, but with the mass market seemingly less interested in blockbusters this summer, can it manage enough cash for another sequel?

Jonah Hex, meanwhile, is going to have a massive job to whip up more than $30m, especially given the weak advance word of mouth, while The Last Airbender, Grown Ups, Salt and The Sorcerer's Apprentice may just need a few more marketing dollars. And that's before we get anywhere near August's releases.

So what's happening? The usual studio line is to blame piracy, and certainly the odd staggering of some release dates is likely to be having some impact. But could - whisper it - we just be getting a little bored of, or at least less excited about, the same-old style of summer blockbuster? Perhaps the acid test for that will be Christopher Nolan's Inception, arguably the only film of the summer that has outright gamble tattooed right over it.

Could it be that, this year, cinema audiences will be less enthused by the cycle of franchises and sequels, and instead choose to back something different and original-looking with their dollars?

We'll be finding that out in July. Before then, though, you can bet that there are some interesting meetings taken place in the boardrooms of Hollywood with the arrival of every fresh set of box office numbers...