If you're a newcomer to the world of Pokemon - go watch the show first. But if you already love the show and the characters you'll really enjoy this movie. I'm usually a purist who'll only watch Japanese anime in its original language with English sub-titles, but I believe the people who dub Pokemon really try to stick the creators vision of the character and the show.
The movie is a little darker, but certainly not too dark for the kiddies, who have to deal with much scarier concepts on TV shows all the time. Mewtwo wants to take over the world sure, but there's no blood and guts and the real serious violence is off screen or implied.
There are battles, but that's what Pokemon is all about. Rest assured - like the series - no-one dies or is even seriously injured.
Like the series the real lessons of the movie (if entertainment must have a lesson) is that friendship is the true strength, and that only by learning to live together can we all truly be happy. Additionally we learn that how and where you are born matters little next to how you live your life. Like the show the movie has strong moral messages even while being bright and entertaining.
And for an adult? Well, I can get lost in the colourful simplicity of this world, the delightful characters and the fun adventures.
Look out for the short film - Pikachu's Vacation - it's great fun too.
By the way, the music for the show is also wonderful.
Go see it! (I also hope that the original Japanese movie will be released with English sub titles someday).