Professor Layton is a game about solving puzzles, a film following the same concept would certainly be interesting, after all I'm sure you realise how bad most game-related films and film-related games are.
Anyone who's played any of the games know how ridiculous the stories are, there's no exception here, as the film progresses things get more and more ridiculous: from the sharks at the start through the chainsaw contraption right up to the final showdown. At least you can't complain it's not original.
Puzzles are there too, not quite as shoehorned in as in the games though, the few puzzles there are in this hour and a half do get you thinking, the was quite some discussion at the screening when the puzzles were asked. And they don't try hiding their nature as puzzles, they are asked as puzzles in the films as they are in the games.
It's a shame the film will have such a cult following, appealing really only to people who have played the games. Fans of the series will undoubtedly enjoy the film, at one point someone gets kicked in the *ahems* and the 'hint coin' noise is added as a sound effect. That doesn't mean non-fans won't enjoy it, just don't expect it to be the most believable film, even anime, you've seen.
Some things are lost in translation; because the film starts in London, the eponymous hero is British and there are a number of references to the UK it's still decidedly Japanese which makes some of the references to being a "British Gentleman" rather humorous. The art style, too, is the same as the games, and the voice acting is taken straight from the series so be warned that Luke is still a main character. "'ello there professor!" The film is more like a feature-length cut scene than a film adaption and while game fans will get more out of the film than those that haven't played any of the series it doesn't mean if you don't know the series it's not worth seeing. It's so ridiculous and over the top it's worth seeing just for that.
I would highly recommend Professor Layton and The Eternal Diva for any fan of the series, any fan of anime and anyone with ninety minutes to spare and wanting something entertaining to watch.
It's better than a lot of films and a lot better than most game/film adaptations. It won't be to everyone's taste but it's ridiculous enough to make it entertaining and memorable.