I'll admit it up front: I've never seen "Jumanji".

Yes, I know, I'm a charlatan. I've (largely) managed to conceal my abject lack of qualification to review movies until this point, but the charade is over: A sequel to the beloved 1995 Robin Williams adventure is almost here, and I don't know whether anyone can enjoy it without knowing anything about the original.

Luckily, you can! "Jumanji: Welcome to the Jungle" is really "Jumanji 2" only in spirit. It gives a light and respectful nod to the original, then gets on with doing its own thing. And to my surprise, despite a few problems, it's a lot of fun.

After a 1980s kid discovers a game called "Jumanji" half-buried on a beach, we flash forward to the present day. Four teenagers go from blackboard jungle to actual jungle when they discover a bizarre game console and find themselves sucked into the video game. Arriving in a cursed rainforest, they must fend off villains and angry animals to complete the game and find a way out, while of course learning a little something about themselves along the way.

The fun is in the casting. The disparate "Breakfast Club" of squabbling teens is teleported not just into a strange game world but also into strange new bodies: exaggerated games characters, played by Dwayne "The Rock" Johnson, Karen Gillan, Kevin Hart and Jack Black. The teens -- a jock, a timid nerd, a vapid social media junkie and er, another timid nerd -- find themselves in the least likely body, and chucklesome gags flow like the Amazon. The stars doing the jungle boogie play entertainingly against type -- Johnson is a hoot, flexing his comic muscles as the brain who's nervous about his newly discovered brawn.

The body-swap concept also teaches the characters important lessons, about looking beyond the appearances of others and understanding themselves. In the jungle -- the mighty jungle -- there's an emphasis on problem-solving and teamwork rather than on violence, as the characters draw on strengths they didn't know they had. So while the selfie-taking air-head is the butt of a few jokes aimed at the pernicious stereotype of a teenage girl, she's also the first to figure out some of the obstacles they face and frequently helps others to overcome their issues when they can't see the metaphorical jungle for the trees.

Frank Masi

Generally, "Welcome to the Jungle" is a pretty upbeat and positive experience, but it still has some odd lurches into clanging tone-deafness. For example, there's a big fight scene that escalates quickly from amusing cartoon slapstick to the Rock straight-up snapping some dude's neck with an audible crack. It's pretty jarring in itself, but it's perhaps worse that there are no consequences and no one mentions it again.

Similarly, the movie just can't help ogling former "Doctor Who" star Karen Gillan in her skimpy outfit. Fans were up in arms when the first picture of the stars revealed Gillan's cropped top and hot pants, prompting the filmmakers to insist there's a good reason in the story for the outfit. And I can reveal that, yes, there is a good reason for the outfit: So we can ogle Gillan.

Maybe it's a comment on sexualised female characters in video games and movies. Maybe it's meant to be body-positive and empowering. But the film can't help undercutting itself: At one point, in a scene that really feels like it was hastily added after the fan reaction, Gillan's character asks for a jacket to cover her skimpy outfit ... then pretty much never wears it. Worst of all, her character's story builds to a big scene that's supposed to be the culmination of her journey to empowerment -- and ends with a loving, lingering close-up on her short-shorted behind.

A jaunt to a vaguely ethnic bazaar is also a bit uncomfortable. And the fact that we're supposed to overlook that one of the black characters is literally a servant to the others is frankly appalling.

The video game concept provides a neat twist on each adventure sequence, having fun with non-player characters, giving our heroes a finite number of lives and creating obstacles that level up in difficulty. The CGI animals are OK, but as the main menace, Bobby Cannavale is a hair-raising villain. You can bet today's kids will look back on his character with a shudder the way yesteryear's kids look back on the scariest films of the 1980s.

Does the sequel surpass the original? I couldn't tell you, for reasons I mentioned earlier. But "Welcome to the Jungle" is a diverting comic caper with plenty of laughs even for viewers new to the world of "Jumanji". And when it comes to a rib-tickling combination of action and comedy, it proves Dwayne Johnson is king of the jungle.

"Jumanji: Welcome to the Jungle" lands in theatres in the US and UK on 20 December and Australia on 26 December.

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