I might not be the best person to review this movie since I've never read the manga or seen the anime, but then again that didn't stop me from falling madly in love with DEATH NOTE and immediately gobbling up the manga, anime and Blu-Rays. I heard about KAIJI because the two stars of DEATH NOTE (Tatsuya Fujiwara and Ken'ichi Matsuyama) reunite in this film and that sounded exciting! And it was, but it was also disappointing because Tatsuya is the main star (and he's great), but Ken'ichi only has a very minor part with probably less then two minutes of actual screen time! WTF?
The story is about this dude who has a crappy job with no fucking future. So he's hard pressed one day by these evil dudes into going on this cruise ship where he's suppose to gamble away his debt to them (whether or not his debt was actually real I never figured out). So he gambles and ends up as a slave for these people and spends 15 years(?) working on some underground construction. Finally one day he get the chance to gamble his way out if slavery and all kinds of wild shit happens.
I liked the story a lot and enjoyed the movie, but it felt like they were just cramming too much into the movie and skipping right over some important shit. My recommendation is to read the manga first then watch the movie. Personally I liked the story enough that I'm going to try and read them myself before I watch Part 2.
Visually though the movie looked really nice and the acting was fun. I especially liked the main bad guy who I'm pretty positive was the finger snap dude from 20TH CENTURY BOYS. He was really good and his character was a complete asshole. I really hope he's back in the sequel.