The death knell was the storyline. After witnessing an epic revenge plot, an epic quest to save the world, and an epic complex story about the Unown, having a plot be a generic "Guy wants to capture Pokemon" plot was extremely underwhelming, and it didn't engage me at all and had several plot holes.
But it wasn't all bad! Mewtwo remained an amazing villain, and his dialogue was outstanding. The animation was good, especially the great ending, and the fights were good throughout (no knock your socks off ones like most of the movies though). There was also some funny bits.
But as a whole, a mediocre movie. However, if you have a greater tolerance for the kind of plot it has, you might get a kick out of it.
