Let’s cut to the chase, shall we? The fourth Indiana Jones movie isn’t as good as 1981’s original Raiders of the Lost Ark but it whips the pants off the two sequels that followed.

It’s taken Steven Spielberg and George Lucas 19 years to come up with an excuse to send our favourite fedora-wearing, snake-phobic archaeologist into the jungle, and it’s tempting, because Indy (like the actor who plays him) is now grey-haired and a little tired around the eyes, to describe the franchise itself as weary. A more accurate word would be complacent. Indiana Jones Part IV exerts itself in fits and starts, but basically conserves its energy because — yes, I’m afraid so — this looks more like a hello than a goodbye.

The first 20 minutes are dynamite, full of fascinating feints and foxing façades. We’re in Nevada, in 1957, and the crisp and creepy visuals are a queer blend of The Wizard of Oz and Invasion of the Body Snatchers.

A beautiful nuclear mushroom cloud eviscerates an “ideal” suburban enclave and its plastic nuclear families. Our hero, forced by the KGB to uncover an alien being, reveals that 10 years earlier he helped uncover evidence of an alien landing but was told he’d be accused of treason if he blabbed. Now he’s about to lose his job at Marshall College, because the McCarthyite boys at the FBI suspect him of being a commie.

“I don’t recognise this country any more,” laments the college dean (Jim Broadbent). The US government, peddling a toxic version of patriotism, wants to blind and gag its own citizens. Sound familiar?

As so often in his career, Spielberg asks us to look at the aliens in our midst with open hearts. Crystal Skull, in fact, contains more than a few echoes of his 1977 masterpiece, Close Encounters of the Third Kind. For their own nefarious reasons the Russians, led by Cate Blanchett’s flinty Irina Spalko, want to return an extraterrestrial crystal skull to a “lost” Pre-Mayan city. Meanwhile, Indy is approached by a greaser teen called Mutt (Shia LaBeouf) whose dad, Professor Oxley (John Hurt), has just gone missing.

The key players all collide in the jungle, and a neat moment has Mutt looking on with disgust while Indy excitedly tries to make sense of a map with Irina. Like the Richard Dreyfuss character in Close Encounters, Indy can’t resist a riddle and gravitates towards fellow obsessives.

Harrison Ford has the sweetest of dry grins and, if it’s not quite as confident these days, it’s still engaging. He and his new sidekick work nicely together. Mutt says Indy knew his mum — Mary — to which our hero responds with a mumble “There were a lot of Marys ...” Later, he tells Mutt, “You don’t have to keep getting sore to prove you’re tough.”

The secret of Ford’s Indy is that however many punches he throws, and however many dames he kisses, he never acts tough. Maybe that’s why it’s so easy to accept him at 65. His brawn has always seemed flukey; it’s his brains we rely on.

The big disappointment comes when his old flame reappears. “Mary” is Marion Ravenwood, the gin-gulping gal played by Karen Allen in Raiders of the Lost Ark — now, their chemistry is non-existent. She is allowed two expressions — a gormless pout and a gormless smile — and gets not a single decent line. Age hasn’t withered Indy but, thanks to Spielberg and his scriptwriters, Marion’s spark has been extinguished.

The minor characters are similarly mistreated. It’s well-known that the franchise pays homage to the adventure serials of the Thirties and Forties, but does the presentation of “people of colour” have to be stuck in such a time warp too?

Crystal Skull isn’t brazenly racist like Temple of Doom, but its jungle-dwelling Peruvians do seem remarkably easy to brush aside. Is it just me or is there something weird about the titular “white” skull, which only communicates with Caucasians and causes natives to bow down in awe? The subliminal message is that the Mayans couldn’t possibly have come up with scientific innovations by themselves: they needed help from white folk, albeit white folk from outer space.

Should Indiana Jones and the Kingdom of the Crystal Skull ever wind up in a museum, future generations may ask themselves a number of questions. Why is it that fist-fights and sword-fights — like drum solos — always last about one minute too long? Why do family movies work so hard to give children nightmares? (Parents should be prepared for a scene in which a man is eaten alive by ants.) Was it wise to make such an issue of Mutt’s quiffy hairdo? (It makes LaBeouf look more like Depeche Mode’s Dave Gahan than ever.) Why is it that Cate Blanchett gets so much work? She lifts her cheekbones up and down nicely but it’s only at the end, when the trippy CGI effects take over and we can barely see her face, that her character makes an impact.

Last but not least, why have we allowed these old-rope merchants, Spiel-berg and Lucas, to dominate our lives for so long? Spalko’s Russians want to control minds and retell history, a feat of daring that George and Steven can pull off with ease — even at half-strength.

Maybe that says more about us than them; we get the gods we deserve. But, watching Crystal Skull, it strikes you that we could have done a lot worse. This is a fun watch: an antiques roadshow that, when it can be bothered, makes time fly.