Kyurem vs. the Sword of Justice is not insulting like some other bad Pokemon sequels. *ahem Celebi* Still, it's completely devoid of any outstanding elements. There's virtually nothing I can praise this work for.
The art quality seems to have slightly decayed since the last film. I'm not sure whether to pin this on use of unremarkable locations or if it's really true. Either way, this not-even-feature-length cartoon, boasts multiple locations we've seen before - albeit, slightly edited this time around. Train sequence in the mountains is a carbon copy of the one in Shaymin's adventure. The city has no features to distinguish it from a dozen of other cities in the Pokemon universe. The only unique location present is Kyurem's arena - and it's not an interesting one to see. While there is some neat coreography in the final battle accompanied by some nice animation, you won't lose yourself in it for longer than a minute. Unbelievable character development and feats clearly summoned by needs of the plot will make you groan. With this faint praise out of the way and music not worthy a mention, lets move to the real problems - characters, dialogue and plot.
"This place is not meant for humans" - Kyurem, warning Ash & company to leave a human built, post industrial era, metal structure.
The biggest problem with the film is Keldeo himself. This pony is insufferable. His personality can be summed up as egoistical, rash and cowardly. The film never attempts to make us care about him, as it asumes we already do. In the same way, film asumes we'll believe in character development which never actually occured. Confession of an obvious lie with no symbolic significance isn't a groundbreaking character moment. In the same way, Ash did a half assed job at helping him, being little more than an audience stand in. He shouldn't've been in the film in the first place. The supporting ponies of justice aren't much better. Each one of them is given a stereotype and little to do except spout exposition. Kyurem himself is not connected to Reshiram and Zekrom in any tangible way and the arbitary idea of making him a traditional enemy of the brony squad seems poorly taught out.
Plotwise, the film boasts a few impressive achievements. This marks the first pokemon sequel in which our heroes trespass, blatantly destroy city property, and then steal airships and trains with no reprecussions whatsoever. It also boasts the surprising achievement of happening at night so that we see no more than three people in the whole city. Beyond that, one of my favorite continuity errors is a malfunction on air ship's engines which lead to its fall... that never occurs because five minutes later Iris is flying as if nothing happened. No explanation given, of course. Obviously, I'm mocking the film in this paragraph. I could've tried explaining the plot, but this paints the picture much more vividly than a boring plot synopsis ever could.
I could ramble on and on, but I don't feel like it. Avoid this film.