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But – well, there is a but.

Two buts, actually, the first being painfully miscast Cate Blanchett. Harrison Ford reprises his role as Indiana Jones with the same wry glint in his eye that we all know and love, Karen Allen returns as Marion Ravenwood, and Shia LeBoeuf pitches in nicely as heir apparent to Indy’s hat. The chemistry is there for the film’s heroes, but Blanchett just can’t make her role as the villainess, never mind her Russian accent, work. She sticks out like a water-deprived fish; her Irina Spalko lacks the sneering flair that allowed Wolf Kahler to chew up his scenes with villainous gusto as the Nazi Colonel Dietrich in “Raiders of the Lost Ark.” In all fairness to Blanchett, though, David Koepp did underwrite the character. Spalko seems like a mere clip-art villain thrown in to keep the plot moving rather than a genuinely pulpy agent of menace.

The disappointment, however, really comes from how closely “Kingdom of the Crystal Skull” hews to “Raiders of the Lost Ark,” right down to the photocopied ending. Sure, the adventure is ripsnorting, and George Lucas’ trip down a memory lane belonging to Erich Von Daniken laced with 1950s sci-fi has a certain appeal to go along with the quaint homage to the Cold War era fear of invading communist body-snatchers. But there’s no gamble in betting on how everything plays out. Gunshots are fired, fists flash, cars swerve, insects swarm, stuff goes boom. Most disheartening: valuable knowledge inevitably gets locked away in government storehouses, obliterated, or rendered otherwise inaccessible. Unlike “National Treasure,” where Ben Gates actually gets to study his discoveries, the “Indiana Jones” films set off to blow stuff up in a quest to ultimately remain ignorant. So much for the science of archaeology. So much for the science fiction of this sci-fi homage.

And there’s a third “but,” too, namely, the film’s single-minded linearity. “Kingdom of the Crystal Skull” is a chase movie, chock-full of wild, and wildly implausible, stunts. Not a mystery, not a puzzle, just an exciting chase that is singularly unconcerned with developing any of the ideas underlying the whisper of a plot and saddled with rather unsubtle direction on Spielberg’s part. Provided expectations are set on fun, “Kingdom of the Crystal Skull” lives up to that first paragraph, but not much more.

Of course, the introduction of LeBoeuf’s character, Mutt, coupled with hints from the Flanneled One, not to mention a groan-inducing clue in the film’s final scene, means we can look forward to a fifth installment. There are worse things than a film satisfied with being a thrill ride, but as fun as “Kingdom of the Crystal Skull” can be, hopefully whatever comes next will be more ambitious.