This movie is a good homage to both series and blends well. Others don't agree.
Other reviews were quick to point out that it was not actually Lupin vs Conan, but rather Lupin & Conan. This is true. However, I don't agree that it's something to bash this movie on. Conan solves mysteries. Lupin the 3rd is already known to be a robber. It's not a mystery. The story had to revolve around a case that Conan would have to solve, and somehow have a treasure that Lupin would steal. The stories in either series were always outlandish in their own way, and this movie was no different. It would fit perfectly in either series.
Also, although Lupin and Conan do not meet each other until right about halfway through the movie, it was not necessary that they meet earlier, and the movie gives plenty of screen time to all characters. Familier faces from both series show up, and no one acts out of character. Fans of both Lupin and Conan can watch this and know that it will not dissapoint them.
Both the art style and the presentation was a good mix of both series. The music was always fitting and taken from the openings. Even the words displayed on screen had a typewriter feel to it, classic Lupin III.
Some Cons to the movie were inevitable. Neither Lupin nor Jigen ever use their handguns, they don't even both to pull them out. It's true that Lupin's style is subterfuge, but at one point Jigen and Goemon take out guards carrying machine guns (who were all bruised up), seemingly with their fists, all off screen. This is only my opinion, but a little bit more action would have been nice. Maybe Jigen could have shot a bullet out of the air, with his bullet. He's known to do that.
Overall, it was exactly what someone would expect from mixing the two together. Mystery, action, comedy, and above all good characters.