All right, I have to admit up front that I'm in love with Haruhi. This review is unavoidably coloured by my attachment to the character.
Even so, this movie is great :) If you haven't watched at least the first season of The Melancholy of Haruhi Suzumiya, go do so now. I'll wait. Done? Good.
After a "normal" day at the SOS Brigade, Kyon wakes up in a world in which Haruhi does not sit behind him in class, apparently no one at Kita High has ever heard of her, and there's no sign of the SOS Brigade. The only glimmer of hope if Nagato, who's the only member of the Literature Club, just as she was before Haruhi found her. Will this be enough to restore Haruhi to the world? Does Kyon even want to? Or would he quite prefer this more prosaic version, without Haruhi's bossing?
No, I'm not going to tell you the ending. Seriously, get this movie and watch it. Don't feel embarrassed if you want to watch it more than once :)
This movie would be part of my (not so small) set of "anime movies you really have to watch", were it not that it's completely impossible to understand on its own. You are supposed to know already who the characters are, their personality and relationships. I know that most movies-from-a-series have this issue, and that trying to introduce the characters again would have bogged down half the movie and bored the fans; still, I can't say "watch this, it's great!" to anyone who hasn't seen the series, I can't use it to introduce people to good anime. This is, essentially, a long episode: if you are not sure you like the series, this movie will quite probably not change your opinion one way or the other; if you like the series, you'll love this movie.
We get to see some new facets of the main characters: Kyon is more active than in the past, and has some interesting, although not very explicit, soul-searching time; Nagato is shy and cute and not sure what to do with her feelings; Mikuru is even more passive and useless than usual; Koizumi is not his reserved and mysterious self. And the big reveal at the end is a very nice piece of character development: although in hindsight it feels almost unavoidable given the personalities and roles in play, it's still interesting and surprising. And the story is peppered with hints that you probably don't get the first time you watch it.
Short version: what are you doing reading this review? Go get and watch the movie!
