Honestly, it wasn't that bad. I give it maybe a 5/10? Have you guys seen the Japanese Death Note movies? Keeping the time limitation in mind, they weren't half bad. The thing is, Death Note's source material has a lot of content. When you adapt it into a movie, you have to cut out a lot. Imagine if A Song of Ice and Fire was adapted into movies instead of a TV show. They would have to cut out so much that enriched the story.
I don't even care if they completely changed the story in an American adaption. If they kept the concept the same, I think it'd be really interesting to see a Western take on the idea. How does the American view on justice differ from Japan's? However, they made a half-assed adaption of the Japanese story, which I don't understand. For one, they butchered the characters. Light and L are both calm and collected, but in this adaption they were anything but. Ryuk specifically states that he's not on any side in the anime/manga, and he dropped the notebook because he was bored, and wanted to see how humans would react to it. However, in this adaption Ryuk eggs Light on to kill someone which goes against everything his character stands for. The worst change in my opinion, however, is the relationship between Light and L. What made the original story so interesting is this cat and mouse chase between the two characters. They both had to constantly outmaneuver each other, but where was that in this adaption? For what it's worth, the ending wasn't that bad. It actually felt like Death Note. If someone who never watched the original show watched this, they might not think it's that bad. But there was so much room for improvement. If Death Note is adapted again in the future, I really hope that it's a TV show, and not a movie.