It's an hour-long tenth anniversary Pokemon TV special, which means 42 minutes if you're watching without adverts. It's fine. You wouldn't drag people to watch it, but it's perfectly okay.
The story involves Mirage Pokemon, i.e. computer-generated replicas that can use any attack they've been programmed with, regardless of the originals' capabilities. They're like solid-light holograms. They also appear and disappear with a vapour trail of pixels, instead of just blinking out as if someone turned off a lightbulb. They don't even have to be copies of a real original, but can choose to copy extinct or mythical Pokemon instead. This is a fun idea, but the way it's been done is a bit nonsensical. The Mirage Master's plan is as follows:
(a) use the Mirage machine to build an invincible "perfect Pokemon". To do this, he thinks he needs exhaustive data on all existing Pokemon, despite the fact that a Mirage's powers are "whatever I want" and its physical appearance is surely more or less the equivalent of a computer's desktop wallpaper.
(b) to this end, the Mirage Master wants all the Pokemon data in Professor Oak (Okido)'s database. Professor Oak obviously doesn't want him to have this, but eventually gives way and tell the villain his database password to stop Pikachu from being mind probed. Dramatic, right? Surprisingly though, what happens next is that the Mirage Master hacks into every Pokemon database in the world and reads all their contents. That's clever. He doesn't even need to do it on-screen. It seems to be just a "press the big red button" job. In that case, what was the point of bullying Professor Oak into handing over all the information voluntarily, when a few minutes later he'd have been hoovering up all the information for himself anyway?
However that said, none of that really matters. This is Pokemon, not a computer science textbook. The story does its job in terms of giving its villain a threatening and ethically dubious plan. The episode's ignoring the parallels, obviously, but this is Nazi-like. It's eugenics, except with computer-generated monsters instead of human sex and babies. The Mirage Master's creations are whiter than white and he sees them entirely in terms of superpowers. Soul, personality and individual identity are undesirable pollutants in his dreams of purity. "That Pokemon's nothing but a flawed specimen!"
What's more, he gets called on this. Professor Oak attacks him on scientific ethics and lack of respect for Pokemon. The plot depends on a Pokemon (Mew) being more than just the Mirage Master's reductive list of stats and powers.
I quite liked all this. It makes for a reasonable 42 minutes. It's in no way reaching greatness, but it's comfortably at the level of "decent television". I enjoyed seeing Mewtwo and Mew again, although of course they're just mirages and so fake-Mewtwo never speaks or shows any personality. Darn. A sympathetic character gets a death scene, waving bye-bye as their body disintegrates into pixels, although the fact that they're only a mirage will mean you're safe from kiddie trauma.
(a) Jessie/Musashi from Team Rocket says "it's showtime", so I had to pause the episode to find and kill a kitten.
(b) Ash/Satoshi has Lassie powers. "Mew mew mew!" "What's that? You're telling me to follow you?"
(c) Misty/Kasumi returns, despite having left Ash/Satoshi's gang and stopped being a regular by this point. This is her last appearance to date, I believe. Her replacements are a girl (May/Haruka) and her little brother (Max/Masato). Why do all those English-language names begin with M?
There are some points of mild interest in the English-language version. Firstly, this was the first Pokemon anime feature to air first in America, not Japan. Secondly, the English-language production was by Pokemon USA and TAJ Productions instead of 4Kids Entertainment, so for instance they kept incidental music from the Japanese movies and series, despite the fact that 4Kids preferred to replace all the music. I like that, but the downside is that they ditched the voice actors. Many of the old voice actors had been doing the show for eight years, but only three of them were judged to make the cut here. Fans were upset, of course. It was subsequently announced at the 2006 San Diego Comic-Con that they'd redo the dub for the DVD, which is the bonus disc of the eighth movie (Lucario and the Mystery of Mew).
Personally I don't mind changes. I do object to the fact that the replacements aren't very good. They're making the dialogue sound bad. In fairness it is, but better actors would have been able to hide the badness better. The new Brock/Takeshi is particularly annoying.
Overall, it's fine. It's not transcending what it is, though. It's merely a good feature episode of a children's cartoon, with occasional minor hiccups that are unlikely to bother the target audience. Mirage Master looks quite nifty, wearing a simplified Rorschach mask with a bigger hat and a cloak with a huge collar. I liked Mew. I liked the fact that the episode's not just empty nonsense, but instead has a bit of thematic content. If you already like Pokemon, I imagine you'll like this.