I'll start by saying I've not seen this film, and so I don't know if it's as much of as mess as this book is. Simply, this story blends the plot of Asterix the Legionary with Asterix the Gladiator, borrowing characters from both stories. Unlike in the original story, we meet Panacea's fiance Tragiccomix at the start of the story and both are taken by the Romans. As far as I can tell, the only reason Panacea was taken was to be a plot point so they could escape from the Romans only to be captured and take Cacofonix's role in Asterix the Gladiator.
The adventure that Asterix and Obelix goes on is a very brief stint in the legion before becoming a gladiator. Some of the gags are lifted straight from the books but the whole thing is really clumsily executed.
The 'artwork' consists of stills from the film, which look really poor printed on a page. On a couple of occasions the narrative text is dropped altogether and there's a frame-by-frame sequence of events. Dogmatix's scene when he recovers the lost magic potion gourd is a double page of pictures.
There was also the misguided idea that the story is told by Asterix and the games masters (who's not even relevant until the second half of the story). It was lazily done, I felt there was little love by the creators of Asterix about this film.
Let's just say I'm glad this only cost my 50p from a charity shop.