An awesome movie that I've seen several times in Japanese and English and I recommend it to everyone.
The movie takes place between episodes 22 and 23 of the series, but you don't really need to have seen much of the series to really enjoy this movie. Though, seeing it all (or at least up to 22) definatly does have it's benefits as far as character relation goes.
The only real down-side about this movie is that I don't think we see enough of Ed. I love Ed and she's one of my favourite characters from the series.
However, Spike is my other favourite character and we get to see plenty of him. =D And he kick some major ass!!