It's the longest animated movie ever made, according to imdb. It's 163 minutes long, the equivalent of seven TV episodes. Instead of two seasons of Haruhi Suzumiya, we now have two and a half seasons. That's a good way of looking at it. It can feel a bit daunting to sit down to a three hour movie, but you wouldn't think twice if this were broken up into episodes. It's simply another animated adaptation of one of the Haruhi Suzumiya novels (the fourth), with a running time similar to Melancholy's and Endless Eight's.
It's also been well received, even by people who hated the TV series. I liked it too, even I'm not quite as enthusiastic as some. It's doing that thing this franchise does of tackling SF premises more calmly and soberly than you'd expect. It's not my favourite animated movie, although a surprising number of people have said that it's theirs.
Here's a random thought, by the way. Maybe the fact that I'm a long-term Doctor Who fan is part of why I didn't get as excited as some about this franchise? It baffles me when people call Doctor Who mental. I can imagine those people having their minds melted by Haruhi Suzumiya, but personally I think the show's more remarkable not for its juxtaposition of SF ideas but for its violation of the form of a serial narrative (out-of-sequence broadcast order, Endless Eight, opening the series with an in-fiction amateur film, etc.)
Anyway, the film's storyline involves... well, guess. There's a clue in the title. We begin with business as normal, with Haruhi organising a Christmas party whether anyone else likes it or not. Kyon then wakes up the next day to find a world he doesn't recognise. Where's Haruhi? Why does no one remember her? Why is he an exception to the general amnesia? Since he's always bitching non-stop about all the trouble Haruhi keeps giving him, should he be happy or sad about having seemingly been transported from hell to heaven? Kyon himself asks all these questions, by the way. Associating with Haruhi makes you genre-savvy (or dead) and so here we get detailed analysis from the characters of the practical difference between a parallel universe and history having been rewritten.
The explanation of all this goes deeper than you might think. The film has a strong plot, I think. It's well-paced. It's not afraid to be staid when it's appropriate, in which it's like the TV series, but the film doesn't feel slow to me and I don't think the pacing would have changed much had this been seven TV episodes after all. There's more than enough plot to support the running time. I wasn't clock-watching at all. On the contrary, at the end I was surprised that the film ended when it did instead of showing us the last piece of the puzzle. (We know what it's going to be, though.)
You'd want to have watched the TV series first. You'd be fine without it, but a huge part of this film is that it's showing us unfamiliar human angles on the regulars. Look at Itsuki in the other universe saying he loves Haruhi, for instance. Now think back to the Endless Eight, in the scene where Koizumi briefly proposed himself as an object of romantic affection for Haruhi before saying that he was just joking (again) and ruling himself out as not good enough. It had to be Kyon. Now ask yourself what must be under all that imperturbable smiling.
Alt-Yuki is a heartbreaker. She's almost as taciturn and retiring as her normal self, but not emotionless. She's shy. She's nervous. She has body language! She likes Kyon a lot, but she can't break out of her shell and open up to him. She bonds us to the altered world and it hurts to think that it might end up unhappening.
And then we have the motives of SPOILER. Think about them. Think about the logic and motivations. The weight being placed on Kyon. Bloody hell.
Perhaps even more important, though, is the humanising of the show's two lead characters, who've also traditionally been the most off-putting. Haruhi is a sociopathic bitch and Kyon is a whiny, negative snarker. That's the negative stereotype and at times it's been pretty near the mark. Here, though, Kyon deconstructs his own attitude to Haruhi as he becomes downright passionate in his efforts to get her back. He's conflicted in his feelings about her, but he really, really wants to look for her. He turns the world upside-down.
As for Haruhi, she still has all of her negative traits, but at the same time it's made very clear that she cares, underneath. She's more likeable. Her eventual reappearance (albeit not in the way you might expect) gives the film a real boost.
I must mention the animation, by the way. I forgot to mention that the animation on The Melancholy of Haruhi Suzumiya TV series has been universally praised as stunning, because I'm not usually too bothered about that kind of thing. This film, though, really is stunning. It's a movie, of course, with a movie's budget. Of course it's going to look good. However it's almost a shock to watch this film after the (already very good) TV series. That's how much more detailed, fluid and expensive it looks.
Despite the SF concept, this story's focus is firmly on its characters. Don't expect wacky comedy, although it's not without humour. It's satisfyingly intelligent. The characters are smart and practical in their attempts to work out what's going on and exactly how things changed. Does the ending cheat? Maybe. Well, it's Haruhi Suzumiya. This show's always gone out of its way to break the rules.
Oh, and imagining yourself in SPOILER's shoes might annihilate you. I want to rewatch this film now. That's saying a lot for a 163-minute film, especially given how infrequently I rewatch anything these days.