I watched this movie after I finished Death Note anime TV series and there were some discrepancies, but overall it doesn't affect the impression as it is rather a spin-off than a sequel it pretends to be. There are two prequel live action films which you can watch or skip before watching "L change the world", the connection is really weak between them.
Acting in this movie can be very different: from nearly perfect L's performance it jumps to a very ungainly FBI agents speeches, from very bad acting of dying villagers to a strangely well articulated lines and cold acting of K (reminds me a telecaster, who was invited for a role but doesn't actually know how to act). In other words it's a mixed experience.
I found one funny thing in the film. When L was standing on the ladder other guys were looking up at him as he was higher than them, but the boy was looking just in front of himself instead of looking up too.
