The Lost City is like the concept of 60 percent incarnate. Depending on where that number appears, 60 percent can be a positive thing. It’s more than halfway there, it’s (slightly) better than average value. But as a test score, it’s a D-. The Lost City is a lot better than a D-, but the whole thing has a feeling of crossing that halfway point on the way to true success and then sort of giving up.

Take the lost city itself. It’s a previously hidden city on an island in the Atlantic that was submerged under volcanic ash, which hardened and left its location a mystery. But there’s some kind of tomb there, and it contains some kind of valuable headdress, or necklace – the particulars don’t really matter. A rich scion of a media family, Abigail Fairfax (Daniel Radcliffe), has decided he must get his hands on the priceless artefact, so he buys the island and kidnaps the romance novelist (Sandra Bullock) whose deceased husband was an archaeologist, and who herself once had an academic knowledge of ancient texts. That means she might be able to translate some parchment to find the location of this tomb.

Oops, that was just plot synopsis and we didn’t get to the “take the lost city itself” part. The lost city of the title is seen – once, maybe? It exists not to be explored, but to create a jumping off point for action comedy hijinks involving caves and henchmen and explosions and leeches and other humorous danger. And the danger is pretty humorous – 60 percent humorous at least. But when something is the title of the movie, you do expect it to feature more prominently than this lost city does here. So it appears they got 60 percent of the way to a title and kind of gave up there too.

We get about 60 percent charisma from Bullock, who’s not yet 60 years old and may continue to do these roles even when she’s on the other side of the landmark age. We also get Channing Tatum returning from a couple years of an acting hiatus, and we’ve missed him – but he hasn’t rediscovered all of his previous charm. Maybe only – you guessed it – 60 percent of it.

The setup is a bit reminiscent of the old Kathleen Turner-Michael Douglas adventure Romancing the Stone. Bullock’s Loretta Sage, forever on the verge of giving up this grocery store novelist’s life that is beneath her, finds herself in the pages of one of her own books. Fairfax takes her to the island by force and chloroform when she doesn’t agree to help him willingly, and coming to save her is the man who has been posing for the covers of her books. That’s Alan (Tatum), whose character is Dash, and whose biceps and mane of long hair recall that notorious cover model with the single-name moniker: Fabio. Except of course Alan’s hair is a wig, and instead of being a confident, macho type, the smitten Alan stammers whenever he’s around Loretta – who resents him for drawing so much attention from her on book tours she doesn’t want to be on anyway.

One juicy surprise – which would be a lot more of a surprise if it weren’t in the trailers – is that Alan is meeting up with a real adventurer, the type Douglas played in Romancing the Stone. He’s a great bit of stunt casting in Brad Pitt, himself now a whisper away from age 60. Loretta’s got another potential saviour taking an interest in her – her literary agent, Beth (Da’Vine Joy Randolph), who has traced Loretta’s phone watch to the middle of the Atlantic Ocean, and is determined to find her cash cow, whether for reasons of friendship or mere publishing profitability.

The Lost City at 85 percent is a rollicking good time. At its current percentage, which I think you know by now, Aaron and Adam Nee’s film is a good time that might occasionally leave you looking around the room, wondering if this is all there is. The ideas for jokes are funny enough, but they’re not very original, and the actual dialogue relies on the sort of semantic bickering that has become a stand-in for humour in modern writer’s rooms. Supposed laughs are derived from Fairfax’s first name, Abigail, which (he claims) is a gender-neutral name – and the fact that his brothers (not pictured) are similarly named, Leslie and Beverly. I guess it’s how we emasculate detestable characters in modern movies without resorting to full-on gay panic.

And yet it is reasonably enjoyable to watch The Lost City. Big stars, beautiful locales (filmed in the Dominican Republic), a few light laughs that could have been better but are still a good enough distraction, a wee bit of peril – The Lost City is a “sure, why not?” movie if ever there was one.

You’ll never forget all the things about it that could have been better. The movie starts with its best conceit, opening on the floor of an ancient temple, where Loretta and Dash are tied up while hundreds of surrounding vipers slither toward them. But before you have a chance to be worried, it becomes clear that this is Loretta’s bad idea about how to finish her current novel, and by saying “Delete, delete, delete” she can make both the snakes and the villainous man standing above them disappear. If only the Nee brothers had found a way to incorporate this as an ongoing gimmick, giving Loretta the power of a god over the characters in her own story.

Yet instead of The Lost City being the mediocre romance novel she doesn’t want to write, whose details she can change with a few keystrokes, it’s a “real” mediocre adventure that could have been a gas with more imaginative writers than either Loretta or the Nee brothers, making more of an attempt to exceed our expectations. Coming in for a landing at three-fifths of a good popcorn movie, it shouldn’t be a surprise that The Lost City earns a ReelGood rating of