It falls flat in a lot of areas and there is no mistaking that, but I'd say with what remains; it's still worth your time.
Summer Wars is first and foremost about family, and the strength that comes with a prideful and close family. It is very much a love-letter to traditional family values and the strength of having pride in your own.
The Jinnouchi family is without a doubt the best part of this movie. The family dynamics and the relationships within are incredibly realistic and even more-so relatable. You follow Kenji, who, like you; is an outsider looking-in on this close family in their get-together, and also like him; you start to fall in love with them all as you learn more and more about many of the characters in the family and their backgrounds. Watching this it filled me with nostalgia of my own family get-togethers and my family is neither Japanese, or this huge. I'd imagine it manages to do this with most viewers, just because of how beautiful the portrayal is and how the beauty of pride in a/your family is a relatable feeling to all, no matter your country. Well that, and all the very relatable family figures...
In this family you've got the strong, very-respected and traditional head of the family: Sakae, mom, and grandma of many; the not-so-respected family-outcast who isn't so close: Wabisuke; the impressionable, angsty teenage girl of the family: Natsuki; the introverted and nerdy teenager: Kazuma; and all the many different aunts and uncles from different backgrounds and walks of life, with their many mischievous little children and few grown-up, aspiring children. All in all, there is four generations of this family that is shown; and the way the show portrays the many dynamics that would come with that is near-perfect, and it all goes a long way in making the film feel very grounded--despite it's absurd, and often unbelievable story--and enjoyable despite it's many shortcomings. The film is about how the pride and love within this huge family brings all these very different people together under one roof and with one goal; to tackle an otherwise very huge, important and seemingly unsolvable problem.
So with this interesting premise, message and lovely portrayal-- where does it go wrong? Well, to put it candidly: this film fails mostly in it's execution of story. Summer Wars wants to have this grounded and relatable portrayal of family; but it also wants a very wacky (and seemingly ill-devised...) story/plot to accompany it, and it ends up at times feeling like two different films that were badly meshed together.
The villain of the story, "Love Machine"; while clearly not the main or secondary focus of the film--is weak as a character and as a result, feels very nonthreatening (which he very much is not supposed to be). He has, that I can remember, no actual lines of dialogue. In the film he is simply meant to represent the damages that disconnect in a family can bring and how pride can be a double-edged sword. And this is not a subtle representation either--the villain feels like a walking, 1-dimensional symbol. NOT like an actual character. And this ends up hurting both the enjoyment you'll get from the film and your interest in the story.
Next, there's the love interest Natsuki... This character isn't much better than the antagonist of the film. The film wants to make you feel for her at a certain sad point, and root for the protagonist, Kenji, in his interest for her; but the character is never really fleshed out much, nor made that like-able. The film starts out with her lying/using Kenji in a rather selfish and thoughtless manner, and then never really gives her a moment to shine or be made redeemable afterwards, so you never really "root" for her or for Kenji's success at winning her love--which makes that whole part of the story also rather pointless and unenjoyable.
Now with these two rather subpar characters out of the way, there is also the case of the writing in this film. It feels very inconsistent. Often you'll find yourself having to refrain from questioning many parts of the story involving OZ and Love Machine, because not too much of what happens with them makes a whole lot of sense. Yeah, you could argue that they didn't go for realism to begin with, but I can't help but feel they wanted to leave a message in here about technology and how the world is depending on it more and more and the strain that could put on traditional family values-- but such a message fails when so much of what happens in the story feels absolutely unbelievable and appears completely illogical to begin with. And with such a realistic and endearing portrayal of family, such an absurd and unrealistic plot just ends up feeling out of place.
I feel like they could have still gone for absurd, but at least tried to make the plot relatively airtight in it's execution, NOT leaving the viewer to constantly wonder just how certain events happened the way they did or why certain characters would do what they did. As the viewer you're thrown between realistic and believable to unrealistic and unbelievable way, way too much; and not in a well-structured way.
With my biggest love and three biggest gripes of this film out of the way, what else is there? Well in-terms of praising it, I'd say on the whole; the film is still somewhat competently made. The art is simple, but still very colourful, beautiful and nice to look at, and the animation feels very fluid. The soundtrack for this film is rarely anything but fitting; to the abstract and sweet background tunes while you watch the family's slice-of-life moments, to the tense and dramatic action-songs. The voice actors also all do great jobs (especially that of Sakae and Wabisuke!) and are definitely responsible for much of the "life" of the family.
Overall I'd say this film is good. It's not bad, but it's not great either; and after finishing it I couldn't help but feel like it really could have been something truly special.
...Would I call this film disappointing? Maybe. But not from my expectations going-in, but from the initial setup and end-payoff. It takes you on a seemingly very promising ride that ends up going a bit too far downhill, and never really recovers.
