All you need to know about all the Indiana Jones sequels can be summed up in a story Lawrence Kasdan told about scriptwriting the kickoff Raiders of the Lost Ark: that in the shooting script there was a stunt sequence in which Harrison Ford's to-be-iconic adventurer was trapped on a doomed aircraft without a parachute, about to crash into a mountainside. But he found an inflatable life raft and deployed it while jumping out. It hit the mountainside and bounced/slid all the way down to safety with Indy aboard. Kasdan and director Steven Spielberg agreed, naaaawwww, that was too much. Audiences would never buy it. Come the smash success of Raiders, and that same nixed sequence was put right back in.

And that's how these movies have gone, souped-up takeoffs on the matinee serials of the 1930s and '40s, raising the bar ever higher with the wild action, occult/mystic treasures, exotic locales and stupendous special effects inconceivable on the old Monogram and Republic backlots. But along the way the imitators sprang up (the Mummy remakes, the National Treasure flicks). Digital software and sets now allow undreamt-of wonders routinely, and in the long interval since the mildly lackluster Indiana Jones and the Last Crusade (1989), the fear is that the Indiana Jones adventures, now with Indiana Jones and the Kingdom of the Crystal Skull, are more follower than leader.

But for most of its first half, you think this fourth Indiana Jones escapade from the Lucas/Spielberg fun factory is going to be a real home run, hitting all the right marks as furiously as the world Whack-a-Mole champ. It lovingly references favorite old characters and details from the series (even George Lucas' dud TV spin-off The Young Indiana Jones Chronicles) and introduces new ones. Part of the appeal is that the material here isn't afraid to acknowledge (how could it not?) the iconic action-hero's advancing age and a world changing around him, a world of rock 'n' roll, campus protests and A-bomb jitters.

At the outset a graying Indiana Jones (Harrison Ford), circa 1957, is caught with his is-he-or-isn't-he-a-traitor partner (Ray Winstone) in a Cold War invasion of a certain household-name secret Nevada desert military installation by KGB commandos. The deliciously old-school commie rat-bastard bad guys here are under the command of a slithery Stalinist scientist-dominatrix (Cate Blanchett makes possibly the best villain this series has ever had - not that she's utilized to fullest advantage, however). While he escapes in show-stopping fashion and returns to academia, Dr. Jones is blacklisted at his college teaching position by McCarthy-era FBI, dogged by the unimpeded Reds, and waylaid by a leather-jacketed dropout teen-rebel named Mutt (Shia LaBeouf). He puts the archaeologist on the trail of the series' latest Astounding Relic, a Mayan crystal skull that a missing colleague (John Hurt) retrieved from a South American lost city.

Somewhere around the halfway point, though, the fun sort of slackens. We, the Russians, Indy and, er, what's-his-name, Mutt go deeper into increasingly digitized jungles and waterfalls and Mayan step-pyramids, and all the nostalgic nifty-'50s atmosphere fades. Instead we're in more familiar territory — Indiana Jones and the Computer-Generated Visual. The f/x take over. Actors are reduced to digital simulcra of themselves, too often reacting to awesome greenscreen/bluescreen pixel jazz we all well know isn't really there. A Shia LaBeouf-bot vine-swinging like SpiderTarzan is a franchise low point. You ever notice all Indiana Jones' romps (except for the underrated Temple of Doom) finish the same way, with the evildoers, after all the stunts and fights, attaining exactly what they want — and not being able to handle it? The slinky Natasha Fatale takeoff, done brilliantly by Blanchett, deserves a better exit.

Bonus points for those early moments though. And for matching Harrison Ford in this one with an age-suitable love interest. There are enough high points to make Indiana Jones and the Kingdom of the Crystal Skull worthwhile for fans, enough grandfathered-in goodwill to raise a real smile, and a hearty thanks for the memories. But hopefully the legendary hat gets hung up after this one.